Check for WXREGEX_USING_BUILTIN rather than WX_NO_REGEX_ADVANCED

No real changes, just get rid of checks for WX_NO_REGEX_ADVANCED which
is rather confusing as it's not defined neither when using the system
library (which doesn't support advanced RE syntax at all), nor when
using PCRE (which always supports it).

src/common/regex.cpp

@@ -69,8 +69,6 @@
 #       define WXREGEX_CONVERT_TO_MB
 #   endif
 
-#   define WX_NO_REGEX_ADVANCED
-
 // There is an existing pcre2posix library which provides regxxx()
 // implementations, but we don't use it because:
 //
@@ -1027,7 +1025,7 @@ bool wxRegExImpl::Compile(wxString expr, int flags)
 
 #if wxUSE_PCRE
 #   define FLAVORS (wxRE_ADVANCED | wxRE_BASIC)
-#elif defined(WX_NO_REGEX_ADVANCED)
+#elif !defined(WXREGEX_USING_BUILTIN)
 #   define FLAVORS wxRE_BASIC
 #else
 #   define FLAVORS (wxRE_ADVANCED | wxRE_BASIC)
@@ -1058,7 +1056,7 @@ bool wxRegExImpl::Compile(wxString expr, int flags)
     int flagsRE = 0;
     if ( !(flags & wxRE_BASIC) )
     {
-#ifndef WX_NO_REGEX_ADVANCED
+#ifdef WXREGEX_USING_BUILTIN
         if (flags & wxRE_ADVANCED)
             flagsRE |= REG_ADVANCED;
         else