Add SKIP_VERSION option to speed up compilation

Makefile

@@ -534,14 +534,22 @@ test: test-all
 .PHONY: test-clean
 test-clean: test-all-clean
 
+ifdef SKIP_VERSION
+SKIP_GIT := yes
+endif
+
 # Generate the version.h file
 ifndef SKIP_GIT
     GIT_VERSION := $(shell git describe --abbrev=6 --dirty --always --tags 2>/dev/null || date +"%Y-%m-%d-%H:%M:%S")
 else
     GIT_VERSION := NA
 endif
+ifndef SKIP_VERSION
 BUILD_DATE := $(shell date +"%Y-%m-%d-%H:%M:%S")
 $(shell echo '#define QMK_VERSION "$(GIT_VERSION)"' > $(ROOT_DIR)/quantum/version.h)
 $(shell echo '#define QMK_BUILDDATE "$(BUILD_DATE)"' >> $(ROOT_DIR)/quantum/version.h)
+else
+BUILD_DATE := NA
+endif
 
 include $(ROOT_DIR)/testlist.mk