Revert "build: avoid defining _GNU_SOURCE"

This reverts commit 2e6a8f260c.

Too many problems for now, such as with OSX and asprintf().

stream/rar.c

@@ -25,9 +25,6 @@
  * Preamble
  *****************************************************************************/
 
-// needed for asprintf()
-#define _GNU_SOURCE
-
 #include <assert.h>
 #include <limits.h>
 #include <stdio.h>

waftools/detections/compiler.py

@@ -17,8 +17,7 @@ def __test_and_add_flags__(ctx, flags):
     ctx.env.CFLAGS += ctx.env.CFLAGS_compiler
 
 def __add_generic_flags__(ctx):
-    ctx.env.CFLAGS += ["-D_ISOC99_SOURCE", "-D_POSIX_C_SOURCE=200809L",
-                       "-D_BSD_SOURCE", "-D_XOPEN_SOURCE=700",
+    ctx.env.CFLAGS += ["-D_ISOC99_SOURCE", "-D_GNU_SOURCE",
                        "-D_LARGEFILE_SOURCE", "-D_FILE_OFFSET_BITS=64",
                        "-D_LARGEFILE64_SOURCE",
                        "-std=c99", "-Wall"]