patch 8.0.1690: not easy to run one test with gvim instead of vim

Problem:    Not easy to run one test with gvim instead of vim.
Solution:   Add VIMTESTTARGET in Makefile.

src/Makefile

@@ -2088,6 +2088,10 @@ benchmark:
 unittesttargets:
 	$(MAKE) -f Makefile $(UNITTEST_TARGETS)
 
+# Swap these lines to run individual tests with gvim instead of vim.
+VIMTESTTARGET = $(VIMTARGET)
+# VIMTESTTARGET = $(GVIMTARGET)
+
 # Execute the unittests one by one.
 unittest unittests: $(RUN_UNITTESTS)
 
@@ -2115,7 +2119,7 @@ test1 \
 	test70 test72 \
 	test85 test86 test87 test88 \
 	test94 test95 test99 test108:
-	cd testdir; rm -f $@.out; $(MAKE) -f Makefile $@.out VIMPROG=../$(VIMTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
+	cd testdir; rm -f $@.out; $(MAKE) -f Makefile $@.out VIMPROG=../$(VIMTESTTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
 
 # Run individual NEW style test.
 # These do not depend on the executable, compile it when needed.
@@ -2312,14 +2316,14 @@ test_arglist \
 	test_alot_latin \
 	test_alot_utf8 \
 	test_alot:
-	cd testdir; rm -f $@.res test.log messages; $(MAKE) -f Makefile $@.res VIMPROG=../$(VIMTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
+	cd testdir; rm -f $@.res test.log messages; $(MAKE) -f Makefile $@.res VIMPROG=../$(VIMTESTTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
 	@if test -f testdir/test.log; then \
 		cat testdir/test.log; \
 	fi
 	cat testdir/messages
 
 newtests:
-	cd testdir; rm -f $@.res test.log messages; $(MAKE) -f Makefile newtestssilent VIMPROG=../$(VIMTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
+	cd testdir; rm -f $@.res test.log messages; $(MAKE) -f Makefile newtestssilent VIMPROG=../$(VIMTESTTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
 	@if test -f testdir/test.log; then \
 		cat testdir/test.log; \
 	fi

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1690,
 /**/
     1689,
 /**/