generic glibc: guard memfd_create & mlock2 declarations

They were introduced in glibc 2.27

lib/libc/include/generic-glibc/bits/mman-shared.h

@@ -50,6 +50,9 @@
 
 __BEGIN_DECLS
 
+// zig patch: check target glibc version
+# if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 27) || __GLIBC__ > 2
+
 /* Create a new memory file descriptor.  NAME is a name for debugging.
    FLAGS is a combination of the MFD_* constants.  */
 int memfd_create (const char *__name, unsigned int __flags) __THROW;
@@ -58,6 +61,8 @@ int memfd_create (const char *__name, unsigned int __flags) __THROW;
    memory.  FLAGS is a combination of the MLOCK_* flags above.  */
 int mlock2 (const void *__addr, size_t __length, unsigned int __flags) __THROW;
 
+#endif /* if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 27) || __GLIBC__ > 2 */
+
 /* Allocate a new protection key, with the PKEY_DISABLE_* bits
    specified in ACCESS_RIGHTS.  The protection key mask for the
    current thread is updated to match the access privilege for the new
@@ -82,4 +87,4 @@ int pkey_mprotect (void *__addr, size_t __len, int __prot, int __pkey) __THROW;
 
 __END_DECLS
 
-#endif /* __USE_GNU */
+#endif /* __USE_GNU */