Kbuild updates for v5.1

- do not generate unneeded top-level built-in.a
 
  - let git ignore O= directory entirely
 
  - optimize scripts/kallsyms slightly
 
  - exclude DWARF info from *.s regardless of config options
 
  - fix GCC toolchain search path for Clang to prepare ld.lld support
 
  - do not generate modules.order when CONFIG_MODULES is disabled
 
  - simplify single target rules and remove VPATH for external module build
 
  - allow to add optional flags to dpkg-buildpackage when building deb-pkg
 
  - move some compiler option tests from Makefile to Kconfig
 
  - various Makefile cleanups
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Merge tag 'kbuild-v5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

Pull Kbuild updates from Masahiro Yamada:

 - do not generate unneeded top-level built-in.a

 - let git ignore O= directory entirely

 - optimize scripts/kallsyms slightly

 - exclude DWARF info from *.s regardless of config options

 - fix GCC toolchain search path for Clang to prepare ld.lld support

 - do not generate modules.order when CONFIG_MODULES is disabled

 - simplify single target rules and remove VPATH for external module
   build

 - allow to add optional flags to dpkg-buildpackage when building
   deb-pkg

 - move some compiler option tests from Makefile to Kconfig

 - various Makefile cleanups

* tag 'kbuild-v5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (40 commits)
  kbuild: remove scripts/basic/% build target
  kbuild: use -Werror=implicit-... instead of -Werror-implicit-...
  kbuild: clean up scripts/gcc-version.sh
  kbuild: remove cc-version macro
  kbuild: update comment block of scripts/clang-version.sh
  kbuild: remove commented-out INITRD_COMPRESS
  kbuild: move -gsplit-dwarf, -gdwarf-4 option tests to Kconfig
  kbuild: [bin]deb-pkg: add DPKG_FLAGS variable
  kbuild: move ".config not found!" message from Kconfig to Makefile
  kbuild: invoke syncconfig if include/config/auto.conf.cmd is missing
  kbuild: simplify single target rules
  kbuild: remove empty rules for makefiles
  kbuild: make -r/-R effective in top Makefile for old Make versions
  kbuild: move tools_silent to a more relevant place
  kbuild: compute false-positive -Wmaybe-uninitialized cases in Kconfig
  kbuild: refactor cc-cross-prefix implementation
  kbuild: hardcode genksyms path and remove GENKSYMS variable
  scripts/gdb: refactor rules for symlink creation
  kbuild: create symlink to vmlinux-gdb.py in scripts_gdb target
  scripts/gdb: do not descend into scripts/gdb from scripts
  ...

init/Kconfig

@@ -13,7 +13,7 @@ config CC_IS_GCC
 
 config GCC_VERSION
 	int
-	default $(shell,$(srctree)/scripts/gcc-version.sh -p $(CC) | sed 's/^0*//') if CC_IS_GCC
+	default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC
 	default 0
 
 config CC_IS_CLANG
@@ -26,6 +26,22 @@ config CLANG_VERSION
 config CC_HAS_ASM_GOTO
 	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
 
+config CC_HAS_WARN_MAYBE_UNINITIALIZED
+	def_bool $(cc-option,-Wmaybe-uninitialized)
+	help
+	  GCC >= 4.7 supports this option.
+
+config CC_DISABLE_WARN_MAYBE_UNINITIALIZED
+	bool
+	depends on CC_HAS_WARN_MAYBE_UNINITIALIZED
+	default CC_IS_GCC && GCC_VERSION < 40900  # unreliable for GCC < 4.9
+	help
+	  GCC's -Wmaybe-uninitialized is not reliable by definition.
+	  Lots of false positive warnings are produced in some cases.
+
+	  If this option is enabled, -Wno-maybe-uninitialzed is passed
+	  to the compiler to suppress maybe-uninitialized warnings.
+
 config CONSTRUCTORS
 	bool
 	depends on !UML
@@ -1114,6 +1130,7 @@ config CC_OPTIMIZE_FOR_PERFORMANCE
 
 config CC_OPTIMIZE_FOR_SIZE
 	bool "Optimize for size"
+	imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED  # avoid false positives
 	help
 	  Enabling this option will pass "-Os" instead of "-O2" to
 	  your compiler resulting in a smaller kernel.