Fix musl build

Fixes

  match.c.text+0x9c): undefined reference to `re_comp'
  match.c.text+0xca): undefined reference to `re_exec'

by forcing to use the 'modern' regex methods implementation instead of
the obsolete re_comp/re_exec ([1]) one?

[1] http://man7.org/linux/man-pages/man3/re_comp.3.html

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

diff -uNr ytree-1.99pl2.orig/match.c ytree-1.99pl2/match.c
--- ytree-1.99pl2.orig/match.c	2019-09-29 12:37:57.000000000 +0200
+++ ytree-1.99pl2/match.c	2019-10-01 19:46:56.193815327 +0200
@@ -10,7 +10,7 @@
 #include "ytree.h"
 
 #if defined( sun ) || defined( linux ) || defined( __NeXT__ ) || defined( OSF1 ) ||  defined( __OpenBSD__ ) || defined(__NetBSD__) || defined( __FreeBSD__ ) || defined( __GNU__ )
-#define HAS_REGEX
+#define HAS_REGCOMP
 #endif
 
 #ifdef linux