Use the bult-in PCRE engine

This makes sure we can use it wherever we built this package and it avoids a bug
where the dynamic dependency is not in libgit2.pc.

Author: carlosmn

ext/rugged/extconf.rb

@@ -14,6 +14,7 @@
 $CFLAGS << " -Wall -Wno-comment"
 
 cmake_flags = [ ENV["CMAKE_FLAGS"] ]
+cmake_flags << "-DREGEX_BACKEND=builtin"
 cmake_flags << "-DUSE_SHA1DC=ON" if with_config("sha1dc")
 
 def sys(cmd)