Merge branch 'rj/clean-speedup'

Speed up 'make clean' on Cygwin.

* rj/clean-speedup:
  Makefile: conditionally include GIT-VERSION-FILE

Author: prati0100

Makefile

@@ -9,7 +9,9 @@ all::
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
+ifneq ($(MAKECMDGOALS),clean)
 -include GIT-VERSION-FILE
+endif
 
 uname_S := $(shell sh -c 'uname -s 2>/dev/null || echo not')
 uname_O := $(shell sh -c 'uname -o 2>/dev/null || echo not')