tools: power/acpi, revert to LD = gcc

Commit 7ed1c1901fe5 (tools: fix cross-compile var clobbering) removed
setting of LD to $(CROSS_COMPILE)gcc. This broke build of acpica
(acpidump) in power/acpi:
 ld: unrecognized option '-D_LINUX'

The tools pass CFLAGS to the linker (incl. -D_LINUX), so revert this
particular change and let LD be $(CC) again. Note that the old behaviour
was a bit different, it used $(CROSS_COMPILE)gcc which was eliminated by
the commit 7ed1c1901fe5. We use $(CC) for that reason.

Fixes: 7ed1c1901fe5 (tools: fix cross-compile var clobbering)
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: 4.16+ <stable@vger.kernel.org> # 4.16+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

tools/power/acpi/Makefile.config

@@ -56,6 +56,7 @@ INSTALL_SCRIPT = ${INSTALL_PROGRAM}
 # to compile vs uClibc, that can be done here as well.
 CROSS = #/usr/i386-linux-uclibc/usr/bin/i386-uclibc-
 CROSS_COMPILE ?= $(CROSS)
+LD = $(CC)
 HOSTCC = gcc
 
 # check if compiler option is supported