Makefile: fix clang warnings due to clang support

Building u-boot tools with clang as a host compiler e.g. on
FreeBSD with `gmake HOSTCC=clang CONFIG_USE_PRIVATE_LIBGCC=y tools`
leads to many warnings [1] for every compiler invocation since
commit 598e2d33. Part of mentioned commit imports linux patches:

 - kbuild: LLVMLinux: Adapt warnings for compilation with clang
 - kbuild: LLVMLinux: Add Kbuild support for building kernel with Clang

No version of clang supports the gcc fno-delete-null-pointer-checks
though, but it is only passed to clang. Gcc does not have the clang
specific Qunused-arguments for the target. Furthermore several
warnings are disabled which aren't encountered in u-boot. Since such
a build has worked for quite some time and works after removing these
changes, just remove the clang specific handling to restore normal
building with clang as hostcc.

[1] Actual warnings
-------------------
  GEN     include/autoconf.mk.dep
arm-freebsd-gcc: unrecognized option '-Qunused-arguments'

  HOSTCC  scripts/basic/fixdep
clang: warning: argument unused during compilation:
                '-fno-delete-null-pointer-checks'

cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>

Makefile

@@ -209,11 +209,6 @@ HOSTCXX      = g++
 HOSTCFLAGS   = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
 HOSTCXXFLAGS = -O2
 
-ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
-HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
-		-Wno-missing-field-initializers -fno-delete-null-pointer-checks
-endif
-
 ifeq ($(HOSTOS),cygwin)
 HOSTCFLAGS	+= -ansi
 endif
@@ -320,15 +315,6 @@ endif
 
 export quiet Q KBUILD_VERBOSE
 
-ifneq ($(CC),)
-ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
-COMPILER := clang
-else
-COMPILER := gcc
-endif
-export COMPILER
-endif
-
 # Look for make include files relative to root of kernel src
 MAKEFLAGS += --include-dir=$(srctree)
 
@@ -539,20 +525,6 @@ endif
 
 KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
 
-ifeq ($(COMPILER),clang)
-KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
-KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
-KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)
-KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
-KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
-# Quiet clang warning: comparison of unsigned expression < 0 is always false
-KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
-# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
-# source of a reference will be _MergedGlobals and not on of the whitelisted names.
-# See modpost pattern 2
-KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
-endif
-
 KBUILD_CFLAGS	+= -g
 # $(KBUILD_AFLAGS) sets -g, which causes gcc to pass a suitable -g<format>
 # option to the assembler.