atomics: readd some emulation

This time it's emulation that's supposed to work (not just dummied out).
Unlike the previous emulation, no mpv code has to be disabled, and
everything should work (albeit possibly a bit slowly). On the other
hand, it's not possible to implement this kind of emulation without
compiler support. We use GNU statement expressions and __typeof__ in
this case.

This code is inactive if stdatomic.h is available.

1 files changed, 6 insertions, 2 deletions

diff --git a/wscript b/wscript
index 5553b23c72..7eed072bb6 100644
--- a/wscript
+++ b/wscript
@@ -149,6 +149,10 @@ main_dependencies = [
         'req': True,
         'fmsg': 'Unable to find pthreads support.'
     }, {
+        'name': 'gnuc',
+        'desc': 'GNU C extensions',
+        'func': check_statement([], "__GNUC__"),
+    }, {
         'name': 'stdatomic',
         'desc': 'stdatomic.h',
         'func': check_libs(['atomic'],
@@ -173,10 +177,10 @@ main_dependencies = [
         'deps_neg': [ 'stdatomic', 'atomic-builtins' ],
     }, {
         'name': 'atomics',
-        'desc': 'compiler support for usable thread synchronization built-ins',
+        'desc': 'stdatomic.h support or emulation',
         'func': check_true,
         'req': True,
-        'deps_any': ['stdatomic', 'atomic-builtins', 'sync-builtins'],
+        'deps_any': ['stdatomic', 'atomic-builtins', 'sync-builtins', 'gnuc'],
     }, {
         'name': 'c11-tls',
         'desc': 'C11 TLS support',