config.mak.uname: add clock_gettime() to the cygwin build

Cygwin supports the clock_gettime() function, along with the associated
CLOCK_MONOTONIC preprocessor symbol. The autoconf and meson builds both
enable the use of those symbols. In order to have the same configuration
for the make builds, add the HAVE_CLOCK_GETTIME and HAVE_CLOCK_MONOTONIC
build variables to the cygwin section of the config.mak.uname file.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ramsay-jones

config.mak.uname

@@ -251,6 +251,8 @@ ifeq ($(uname_O),Cygwin)
         endif
 	HAVE_DEV_TTY = YesPlease
 	HAVE_GETDELIM = YesPlease
+	HAVE_CLOCK_GETTIME = YesPlease
+	HAVE_CLOCK_MONOTONIC = YesPlease
 	HAVE_ALLOCA_H = YesPlease
 	NEEDS_LIBICONV = YesPlease
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes