Merge branch 'fix/virgile/no-pragma-in-oracles' into 'master'

[libc] Don't keep needless pragmas when cplusplus is not activated.

Closes #717

See merge request frama-c/frama-c!2504

share/libc/features.h

@@ -34,7 +34,7 @@
 #define __POP_FC_STDLIB
 #endif
 
-#ifdef __clang__
+#if defined(__clang__) && defined(__cplusplus)
 # define __CLANG_IGNORE_ATTRS_PUSH__ \
 _Pragma("clang diagnostic push") \
 _Pragma("clang diagnostic ignored \"-Wunknown-attributes\"")