There is no _nl_msg_cat_cntr in musl libc and optimizations
based upon its unchanged value are not possible.

--- a/snapper/Regex.cc	2014-01-29 16:48:30.000000000 +0100
+++ b/snapper/Regex.cc	2015-08-30 11:07:34.613193993 +0200
@@ -22,7 +22,9 @@
 
 #include "snapper/Regex.h"
 
+#if defined(__GLIBC__)
 extern int _nl_msg_cat_cntr;
+#endif
 
 
 namespace snapper
@@ -34,7 +36,9 @@
       nm (cflags & REG_NOSUB ? 0 : nm)
 {
     regcomp (&rx, pattern, cflags);
+#if defined(__GLIBC__)
     my_nl_msg_cat_cntr = _nl_msg_cat_cntr;
+#endif
     rm = new regmatch_t[nm];
 }
 
@@ -45,7 +49,9 @@
       nm (cflags & REG_NOSUB ? 0 : nm)
 {
     regcomp (&rx, pattern.c_str (), cflags);
+#if defined(__GLIBC__)
     my_nl_msg_cat_cntr = _nl_msg_cat_cntr;
+#endif
     rm = new regmatch_t[nm];
 }
 
@@ -60,11 +66,15 @@
 bool
 Regex::match (const string& str, int eflags) const
 {
+#if defined(__GLIBC__)
     if (my_nl_msg_cat_cntr != _nl_msg_cat_cntr) {
+#endif
 	regfree (&rx);
 	regcomp (&rx, pattern.c_str (), cflags);
+#if defined(__GLIBC__)
 	my_nl_msg_cat_cntr = _nl_msg_cat_cntr;
     }
+#endif
 
     last_str = str;