buildgcc: Remove the warning options unsupported by cygwin

My cygwin hostcc doesn't support
-Wempty-body -Waddress -Wmissing-field-initializers

Change-Id: I879e05f3bd396b36b327f204252e820552b6e12e
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: zbao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/1426
Tested-by: build bot (Jenkins)
Reviewed-by: Anton Kochkov <anton.kochkov@gmail.com>

util/crossgcc/patches/acpica-unix-20120420_unknown_warnings.patch

@@ -1,12 +1,16 @@
 --- acpica-unix-20120420/source/compiler/Makefile	2012-04-21 04:02:33.000000000 +0800
-+++ acpica-unix-20120420/source/compiler/Makefile	2012-08-08 16:30:14.000000000 +0800
-@@ -261,15 +261,11 @@
++++ acpica-unix-20120420/source/compiler/Makefile	2012-08-08 18:06:11.000000000 +0800
+@@ -257,19 +257,12 @@
+ # gcc 4+ flags
+ #
+ CWARNINGFLAGS += \
+-    -Waddress \
      -Waggregate-return \
      -Wchar-subscripts \
-     -Wempty-body \
+-    -Wempty-body \
 -    -Wlogical-op \
      -Wmissing-declarations \
-     -Wmissing-field-initializers \
+-    -Wmissing-field-initializers \
 -    -Wmissing-parameter-type \
      -Wnested-externs \
 -    -Wold-style-declaration \