cgit.mk: Use SHELL_PATH_SQ to run gen-version.sh

On some platforms (notably Solaris) /bin/sh doesn't support enough of
POSIX for gen-version.sh to run.  Git's Makefile provides SHELL_PATH_SQ
to address this issue so we just have to use it.

Signed-off-by: John Keeping <john@keeping.me.uk>

cgit.mk

@@ -9,7 +9,7 @@ CGIT_PREFIX = ../
 # main Makefile - they are defined there.
 
 $(CGIT_PREFIX)VERSION: force-version
-	@cd $(CGIT_PREFIX) && ./gen-version.sh "$(CGIT_VERSION)"
+	@cd $(CGIT_PREFIX) && '$(SHELL_PATH_SQ)' ./gen-version.sh "$(CGIT_VERSION)"
 -include $(CGIT_PREFIX)VERSION
 .PHONY: force-version