kbuild: terminate Kconfig when $(CC) or $(LD) is missing

If the compiler specified by $(CC) is not present, the Kconfig stage
sprinkles 'not found' messages, then succeeds.

  $ make CROSS_COMPILE=foo defconfig
  /bin/sh: 1: foogcc: not found
  /bin/sh: 1: foogcc: not found
  *** Default configuration is based on 'x86_64_defconfig'
  ./scripts/gcc-version.sh: 17: ./scripts/gcc-version.sh: foogcc: not found
  ./scripts/gcc-version.sh: 18: ./scripts/gcc-version.sh: foogcc: not found
  ./scripts/gcc-version.sh: 19: ./scripts/gcc-version.sh: foogcc: not found
  ./scripts/gcc-version.sh: 17: ./scripts/gcc-version.sh: foogcc: not found
  ./scripts/gcc-version.sh: 18: ./scripts/gcc-version.sh: foogcc: not found
  ./scripts/gcc-version.sh: 19: ./scripts/gcc-version.sh: foogcc: not found
  ./scripts/clang-version.sh: 11: ./scripts/clang-version.sh: foogcc: not found
  ./scripts/gcc-plugin.sh: 11: ./scripts/gcc-plugin.sh: foogcc: not found
  init/Kconfig:16:warning: 'GCC_VERSION': number is invalid
  #
  # configuration written to .config
  #

Terminate parsing files immediately if $(CC) or $(LD) is not found.
"make *config" will fail more nicely.

  $ make CROSS_COMPILE=foo defconfig
  *** Default configuration is based on 'x86_64_defconfig'
  scripts/Kconfig.include:34: compiler 'foogcc' not found
  make[1]: *** [scripts/kconfig/Makefile;82: defconfig] Error 1
  make: *** [Makefile;557: defconfig] Error 2

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/Makefile b/Makefile
index ba9f41f..9542165 100644
--- a/Makefile
+++ b/Makefile
@@ -537,7 +537,7 @@
 # Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile.
 # CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
 # and from include/config/auto.conf.cmd to detect the compiler upgrade.
-CC_VERSION_TEXT = $(shell $(CC) --version | head -n 1)
+CC_VERSION_TEXT = $(shell $(CC) --version 2>/dev/null | head -n 1)
 
 ifeq ($(config-targets),1)
 # ===========================================================================
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index 87ff1dc..0b267fb 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -18,6 +18,10 @@
 # Return y if <command> exits with 0, n otherwise
 success = $(if-success,$(1),y,n)
 
+# $(failure,<command>)
+# Return n if <command> exits with 0, y otherwise
+failure = $(if-success,$(1),n,y)
+
 # $(cc-option,<flag>)
 # Return y if the compiler supports <flag>, n otherwise
 cc-option = $(success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null)
@@ -26,5 +30,9 @@
 # Return y if the linker supports <flag>, n otherwise
 ld-option = $(success,$(LD) -v $(1))
 
+# check if $(CC) and $(LD) exist
+$(error-if,$(failure,command -v $(CC)),compiler '$(CC)' not found)
+$(error-if,$(failure,command -v $(LD)),linker '$(LD)' not found)
+
 # gcc version including patch level
 gcc-version := $(shell,$(srctree)/scripts/gcc-version.sh $(CC))