libregex: Add a symbol map

kib points out that trying to re-use symbol versioning from libc is dirty
and wrong. The implementation in libregex is incompatible by design with the
implementation in libc. Using the symbol versions from libc can and likely
will cause confusions for linkers and bring unexpected behavior for
consumers that unwillingly (transitively) link against libregex.

Reported by:	kib

lib/libregex/Makefile

@@ -9,9 +9,11 @@ SHLIB_MINOR=	0
 
 CFLAGS+=	-DLIBREGEX
 LIBC_SRCTOP=	${.CURDIR:H}/libc
-SYMBOL_MAPS=	${SYM_MAPS}
 WARNS?=	2
 
+VERSION_DEF=	${.CURDIR}/Versions.def
+SYMBOL_MAPS=	${.CURDIR}/Symbol.map
+
 #HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
 

lib/libregex/Symbol.map

@@ -0,0 +1,16 @@
+/*
+ * $FreeBSD$
+ */
+
+/*
+ * libregex uses a different version name because its symbols are not strictly
+ * compatible with those provided by libc. Re-using the version name from libc
+ * could cause linking headaches and make debugging more difficult than it needs
+ * to be.
+ */
+LIBREGEX_1.0 {
+	regcomp;
+	regerror;
+	regexec;
+	regfree;
+};

lib/libregex/Versions.def

@@ -0,0 +1,5 @@
+# $FreeBSD$
+
+LIBREGEX_1.0 {
+};
+