MINOR: show Built with PCRE version

Inspired by PCRE's pcre_version.c and improved with Willy's
suggestions. Reusable parts have been added to
include/common/standard.h.

include/common/standard.h

@@ -1140,4 +1140,13 @@ static inline void *my_realloc2(void *ptr, size_t size)
 	return ret;
 }
 
+/* HAP_STRING() makes a string from a literal while HAP_XSTRING() first
+ * evaluates the argument and is suited to pass macros.
+ *
+ * They allow macros like PCRE_MAJOR to be defined without quotes, which
+ * is convenient for applications that want to test its value.
+ */
+#define HAP_STRING(...) #__VA_ARGS__
+#define HAP_XSTRING(...) HAP_STRING(__VA_ARGS__)
+
 #endif /* _COMMON_STANDARD_H */

src/haproxy.c

@@ -352,6 +352,9 @@ void display_build_opts()
 #endif
 
 #ifdef USE_PCRE
+	printf("Built with PCRE version : %s\n", (HAP_XSTRING(Z PCRE_PRERELEASE)[1] == 0)?
+		HAP_XSTRING(PCRE_MAJOR.PCRE_MINOR PCRE_DATE) :
+		HAP_XSTRING(PCRE_MAJOR.PCRE_MINOR) HAP_XSTRING(PCRE_PRERELEASE PCRE_DATE));
 	printf("Running on PCRE version : %s", pcre_version());
 	printf("\nPCRE library supports JIT : ");
 #ifdef USE_PCRE_JIT