REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2563

This patch is to fix a incremental build regression bug
which happen when using nmake. That's introduced by 818283de

.

If there is white space before !INCLUDE instruction, nmake will not
process it. Source code's dependent header files are listed in
${deps_file} file, if it's not included successfully, nmake will
not detect the change of those header file.

This patch has been verified in Windows with VS2015 and Linux with GCC5.
The header file add/modify/delete can trig the incremental build with this fix.
There is no impact on the clean build.

Cc: Andrew Fish <afish@apple.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Tested-by: Liming Gao <liming.gao@intel.com>