BUILD: compiler: define __builtin_prefetch() for tcc

We're using a few occurrences of __builtin_prefetch() but tcc doesn't
know about it so let's give it a dummy definition. Now the code builds
and works again with tcc without thread support.

Author: wtarreau

include/haproxy/compiler.h

@@ -264,6 +264,11 @@
 #endif
 #endif
 
+/* Define the missing __builtin_prefetch() for tcc. */
+#if defined(__TINYC__)
+#define __builtin_prefetch(addr, ...) do { } while (0)
+#endif
+
 #ifndef __GNUC_PREREQ__
 #if defined(__GNUC__) && !defined(__INTEL_COMPILER)
 #define __GNUC_PREREQ__(ma, mi) \