kbuild: fix broken builds because of GZIP,BZIP2,LZOP variables

Redefine GZIP, BZIP2, LZOP variables as KGZIP, KBZIP2, KLZOP resp.
GZIP, BZIP2, LZOP env variables are reserved by the tools. The original
attempt to redefine them internally doesn't work in makefiles/scripts
intercall scenarios, e.g., "make GZIP=gzip bindeb-pkg" and results in
broken builds. There can be other broken build commands because of this,
so the universal solution is to use non-reserved env variables for the
compression tools.

Fixes: 8dfb61dcbace ("kbuild: add variables for compression tools")
Signed-off-by: Denis Efremov <efremov@linux.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/Makefile b/Makefile
index 839f9fe..e43d193 100644
--- a/Makefile
+++ b/Makefile
@@ -458,27 +458,13 @@
 PYTHON3		= python3
 CHECK		= sparse
 BASH		= bash
-GZIP		= gzip
-BZIP2		= bzip2
-LZOP		= lzop
+KGZIP		= gzip
+KBZIP2		= bzip2
+KLZOP		= lzop
 LZMA		= lzma
 LZ4		= lz4c
 XZ		= xz
 
-# GZIP, BZIP2, LZOP env vars are used by the tools. Support them as the command
-# line interface, but use _GZIP, _BZIP2, _LZOP internally.
-_GZIP          := $(GZIP)
-_BZIP2         := $(BZIP2)
-_LZOP          := $(LZOP)
-
-# Reset GZIP, BZIP2, LZOP in this Makefile
-override GZIP=
-override BZIP2=
-override LZOP=
-
-# Reset GZIP, BZIP2, LZOP in recursive invocations
-MAKEOVERRIDES += GZIP= BZIP2= LZOP=
-
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
 		  -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)
 NOSTDINC_FLAGS :=
@@ -526,7 +512,7 @@
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
-export _GZIP _BZIP2 _LZOP LZMA LZ4 XZ
+export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
@@ -1047,7 +1033,7 @@
 mod_compress_cmd = true
 ifdef CONFIG_MODULE_COMPRESS
   ifdef CONFIG_MODULE_COMPRESS_GZIP
-    mod_compress_cmd = $(_GZIP) -n -f
+    mod_compress_cmd = $(KGZIP) -n -f
   endif # CONFIG_MODULE_COMPRESS_GZIP
   ifdef CONFIG_MODULE_COMPRESS_XZ
     mod_compress_cmd = $(XZ) -f