[glib: 1/2] meson: Define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 on GNU/Linux if needed

[Philip Withnall <pwithnall src gnome org>]

commit 4e058a698afdf892f1ee2692a4b818e4ded03570
Author: Simon McVittie <smcv collabora com>
Date:   Tue Oct 30 17:20:34 2018 +0000

    meson: Define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 on GNU/Linux if needed
    
    armv5 Linux systems implement __sync_bool_compare_and_swap() and
    friends by calling a function provided by the kernel. This is not
    technically an atomic intrinsic, so gcc doesn't define
    __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 in this case, but it's good
    enough for us. Extend the current Android special case to cover
    GNU/Linux too.
    
    The possibilities are:
    
    * __sync_foo detected and __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 predefined:
      calls to __atomic_foo or __sync_foo primitives are inlined into user
      code by gatomic.h
    
    * __sync_foo detected but __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 not
      predefined: user code has an extern reference to g_atomic_foo(),
      which calls __atomic_foo or __sync_foo because we defined
      __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 when compiling GLib itself
    
    * Windows: user code has an extern reference to g_atomic_foo(),
      which calls InterlockedFoo()
    
    * !defined(G_ATOMIC_LOCK_FREE): user code has an extern reference to
      g_atomic_foo(), which emulates atomic operations with a mutex
    
    Signed-off-by: Simon McVittie <smcv collabora com>
    Closes: #1576

 meson.build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index e642ae227..3af08f866 100644
--- a/meson.build
+++ b/meson.build
@@ -1575,8 +1575,8 @@ atomicdefine = '''
 # We know that we can always use real ("lock free") atomic operations with MSVC
 if cc.get_id() == 'msvc' or cc.links(atomictest, name : 'atomic ops')
   have_atomic_lock_free = true
-  if host_system == 'android' and not cc.compiles(atomicdefine, name : 'atomic ops define')
-    # When building for armv5 on Android, gcc 4.9 provides
+  if (host_system == 'android' or host_system == 'linux') and not cc.compiles(atomicdefine, name : 'atomic 
ops define')
+    # When building for armv5 on Linux, gcc provides
     # __sync_bool_compare_and_swap but doesn't define
     # __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
     glib_conf.set('__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4', true)