build: set _GNU_SOURCE for Adroid

ggml/src/CMakeLists.txt

@@ -1247,7 +1247,7 @@ endif()
 
 # Data types, macros and functions related to controlling CPU affinity and
 # some memory allocation are available on Linux through GNU extensions in libc
-if (CMAKE_SYSTEM_NAME MATCHES "Linux")
+if (CMAKE_SYSTEM_NAME MATCHES "Linux" OR CMAKE_SYSTEM_NAME MATCHES "Android")
     add_compile_definitions(_GNU_SOURCE)
 endif()
 

ggml/src/ggml.c

@@ -144,10 +144,6 @@ static int sched_yield (void) {
 }
 #else
 
-#ifndef __USE_GNU
-#define __USE_GNU
-#endif
-
 #include <pthread.h>
 #include <stdatomic.h>
 #include <sched.h>