Move PCRE2_CODE_UNIT_WIDTH to vre_pcre2.h

We need to ensure that vmods use the same functions and data
types as varnish-cache.

Also it seems that having the define in autoconf might suggest
that it could be changed, which would be misleading.

configure.ac

@@ -138,7 +138,6 @@ else
 fi
 AC_SUBST(PCRE2_CFLAGS)
 AC_SUBST(PCRE2_LIBS)
-AC_DEFINE([PCRE2_CODE_UNIT_WIDTH], [8], [Work with 8-bit characters for PCRE2])
 
 save_LIBS="${LIBS}"
 LIBS="${LIBS} ${PCRE2_LIBS}"

include/vre_pcre2.h

@@ -38,6 +38,8 @@
 #ifndef VRE_PCRE2_H_INCLUDED
 #define VRE_PCRE2_H_INCLUDED
 
+#define PCRE2_CODE_UNIT_WIDTH 8
+
 #include <pcre2.h>
 
 pcre2_code *VRE_unpack(const vre_t *code);