Makefile: Improve generated_defconfig file handling

Commit 2027e99e61aa ("Makefile: Run defconfig files through the C
preprocessor") adds `generated_defconfig' file, but fails to clean that
up. It might be useful to have that file around after `make' is done,
but it's better to clean that up on `make clean'. Also we probably want
to hide it in `git status' list. This patch makes the described changes,
and also adds `-P' parameter to the CPP command that produces the
`generated_defconfig' to avoid generating linemarkers.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Fixes: 2027e99e61aa ("Makefile: Run defconfig files through the C preprocessor")
Acked-by: Andrew Davis <afd@ti.com>
diff --git a/Makefile b/Makefile
index 28a2a1d..91afee6 100644
--- a/Makefile
+++ b/Makefile
@@ -2233,6 +2233,7 @@
 		-o -name modules.builtin -o -name '.tmp_*.o.*' \
 		-o -name 'dsdt_generated.aml' -o -name 'dsdt_generated.asl.tmp' \
 		-o -name 'dsdt_generated.c' \
+		-o -name 'generated_defconfig' \
 		-o -name '*.efi' -o -name '*.gcno' -o -name '*.so' \) \
 		-type f -print | xargs rm -f