Makefile: unexport RUBYOPT

On Gentoo systems with ruby installed RUBYOPT is set and causes build
breakage for some packages that needs host-ruby (example: webkit).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

Makefile

@@ -180,6 +180,9 @@ unexport PKG_CONFIG_SYSROOT_DIR
 # steps of some packages.
 unexport DESTDIR
 
+# Causes breakage with packages that needs host-ruby
+unexport RUBYOPT
+
 # bash prints the name of the directory on 'cd <dir>' if CDPATH is
 # set, so unset it here to not cause problems. Notice that the export
 # line doesn't affect the environment of $(shell ..) calls, so