Allow us to build a semi-dynamic official binary that works back to CentOS 6, at least on x64, and is very fast since we can build it with newer clang or icc.

ext/misc/linux-old-glibc-compat.c

@@ -0,0 +1,18 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+__asm__(".symver memcpy,memcpy@GLIBC_2.2.5");
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern void *__wrap_memcpy(void *dest,const void *src,size_t n)
+{
+  return memcpy(dest,src,n);
+}
+
+#ifdef __cplusplus
+}
+#endif