Add workaround for failing clang build

src/CMakeLists.txt

@@ -645,6 +645,11 @@ else()
 		endif(HAS_UNUSED_BUT_SET_VARIABLE_WARNING)
 	endif()
 
+	if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+		# clang does not understand __extern_always_inline but libc headers use it
+		set(OTHER_FLAGS "${OTHER_FLAGS} \"-D__extern_always_inline=extern __always_inline\"")
+	endif()
+
 	if(MINGW)
 		set(OTHER_FLAGS "-mthreads -fexceptions")
 	endif()