Before, sub-makes called by make were called without make knowing they
were sub-makes. This however led make's jobserver not do its tasks,
and the build process ended up with inefficient parralelisation. This
commit fixes this by applying the two ways the make manual tells
about: putting + to the start of the line (used when ndk-build is
invoked), and exchanging "make" with "$(MAKE)".

Before, make complained with messages like:

make[2]: warning: jobserver unavailable: using -j1.  Add `+' to parent make rule.

This complaint can now only been seen for openssl. openssl has issues
if make gets exchanged with $(MAKE): if exchanged, above error message
is multiplied for various subdirs of the openssl source tree.

On a 4 core box, "make -j 4" build time from "make clean_all" cleaned
source tree could be improved from 15:34 minutes to 10:45 minutes.
This means a speedup of 45%.

dcb91cf0 hacked around the biggest issue
this caused, but wasted a lot of CPU time and disk space  It also still
included a lot of other unwanted files.  This removes all of `doc/` except
the license, and also removes the server list.

Fix android build since commit

696148e2 "Fix Event implementation"

by @ShadowNinja.

Fixes #3444. Thanks @kwolekr for pointing out the fix.

Recent irrlicht revisions break the build, hardcode the revision to a working one
until upstream publishes a working version. See issue #3366 for
a discussion about this.

Also update dependencies to current versions.

Fixes #3291

Thanks to @arpruss for reporting the bug, and suggesting the fix.

Also, remove trailing whitespaces.

Google code was shut down, project moved to github.

  * Rename everything.
    * Strip J prefix.
    * Change UpperCamelCase functions to lowerCamelCase.
  * Remove global (!) semaphore count mutex on OSX.
  * Remove semaphore count getter (unused, unsafe, depended on internal
    API functions on Windows, and used a hack on OSX).
  * Add `Atomic<type>`.
  * Make `Thread` handle thread names.
  * Add support for C++11 multi-threading.
  * Combine pthread and win32 sources.
  * Remove `ThreadStarted` (unused, unneeded).
  * Move some includes from the headers to the sources.
  * Move all of `Event` into its header (allows inlining with no new includes).
  * Make `Event` use `Semaphore` (except on Windows).
  * Move some porting functions into `Thread`.
  * Integrate logging with `Thread`.
  * Add threading test.

Before, android versionName was set to "...13", which made the f-droid build fail.

Previously, sound failed due to errors with hardfp abi build
instructions. As the problem couldn't be found, the softfp
compatible abi was chosen instead.

This move will cause a small performance overhead, but due to the
abi being armeabi-v7a, the internal calculations will still be done
using the FPU.

We also fix some issues with ABI information passing. However, the
fixes aren't sufficient to get sound working.

The patch also fixes an issue with the gitignore file.

Before, android_version.h got changed at every new commit. Now, we
only change it with new minetest releases. Analogous to how cmake
does it,  we add an android_version_githash.h file that communicates
the git hash to C++ code.

Also, unify VERS_MAJOR, VERS_MINOR and VERS_PATCH variable
calculation inside the whole makefile.

Speeding up rebuild:

Before, we've written the android_version.h file at every rebuild.
As it thought the file's content has changed, make has rebuilt files
in the source tree that depended on that header file during rebuild,
causing lots of files being rebuilt without there being a reason.

The reasoning of make can be observed by passing -d and V=1 params
to the ndk-build command. You then got logging entries like:

Prerequisite `jni/src/android_version.h' is newer than target `obj/local/armeabi-v7a-hard/objs-debug/minetest/jni/src/areastore.o'.

Preventing race condition build fail:

Before, there was a race condition, where, if the prep_srcdir target
was executed in parallel with the $(ROOT)/jni/src/android_version.h
one, it could happen that the jni/src directory was nonexistent, and
we were trying to write into a file inside. This resulted in a build
failue:

/bin/sh: 1: cannot create [...]/jni/src/android_version.h: Directory nonexistent

Additionally, we now don't remove the link to src/ needlessly anymore.
Keeping this wouldn't have affected the rebuild, but this way its
more proper.

Also make only one >-redirection, sparing repetition.
Also, use cut instead of awk, which is shorter and should be a bit faster.

Before, our libiconv build was a joke. We first called configure for our own build host system,
then called make, before we executed a Android.mk script we provided as patch. The first "native make"
always failed, and the LIBICONV_LIB file setting in our Makefile didn't match the built one,
resulting in an always-rebuild of iconv.

This commit cleans up this total mess, removes the double-build, and the Android.mk, and properly calls
./configure with the according target platform, and uses a built toolchain.

As we have to deal with the android bug "NDK: Support for prebuild libs with full sonames"
https://code.google.com/p/android/issues/detail?id=55868
as the 2013 patch
https://lists.gnu.org/archive/html/libtool-patches/2013-06/msg00002.html
by Google's David Turner wasn't inside the 2011 libtool, we pass -avoid-version to
libtool.

Thanks to the proper build, wide_to_utf8 works for android now, removing us of the need to disable it.

Fix commenting happening thanks to missing quotes and dereference variable the right way,
to get rid of a compile error.

Due to compatibility concerns, this is temporarily disabled.

Android terminated immediately after start since commit
181f7baa
because library wasn't loaded, and libminetest.so required
libgmp.so.10 instead of libgmp.so.

The second issue has been solved by the linker flags.

Adds everything needed for SRP (and everything works too),
but still deactivated, as protocol v25 init packets aren't final yet.
Can be activated by changing the LATEST_PROTOCOL_VERSION header to 25
inside networkprotocol.h.

Uses system provided libgmp if found, if not it falls back to mini-gmp.

Improve schematic file-saving interface
Add ability to create temporary test files

Minor misc. NodeResolver cleanups
Prefix faux content type constants for testing with t_ to avoid
confusion or name collisions

Make sure to include random unittests in android builds, too
Use SWAP() macro
Ensure that negative ranges are tested as well in random unittests

Split unit tests into separate files under src/unittest/
Give better unittest diagnostics
Clean up some code

Move debug streams to log.cpp|h

Move GUI-related globals to clientlauncher

Move g_settings and g_settings_path to settings.cpp|h

Move g_menuclouds to clouds.cpp|h

Move g_profiler to profiler.cpp|h