Kbuild updates for v5.17

- Add new kconfig target 'make mod2noconfig', which will be useful to
    speed up the build and test iteration.
 
  - Raise the minimum supported version of LLVM to 11.0.0
 
  - Refactor certs/Makefile
 
  - Change the format of include/config/auto.conf to stop double-quoting
    string type CONFIG options.
 
  - Fix ARCH=sh builds in dash
 
  - Separate compression macros for general purposes (cmd_bzip2 etc.) and
    the ones for decompressors (cmd_bzip2_with_size etc.)
 
  - Misc Makefile cleanups
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Merge tag 'kbuild-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

Pull Kbuild updates from Masahiro Yamada:

 - Add new kconfig target 'make mod2noconfig', which will be useful to
   speed up the build and test iteration.

 - Raise the minimum supported version of LLVM to 11.0.0

 - Refactor certs/Makefile

 - Change the format of include/config/auto.conf to stop double-quoting
   string type CONFIG options.

 - Fix ARCH=sh builds in dash

 - Separate compression macros for general purposes (cmd_bzip2 etc.) and
   the ones for decompressors (cmd_bzip2_with_size etc.)

 - Misc Makefile cleanups

* tag 'kbuild-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (34 commits)
  kbuild: add cmd_file_size
  arch: decompressor: remove useless vmlinux.bin.all-y
  kbuild: rename cmd_{bzip2,lzma,lzo,lz4,xzkern,zstd22}
  kbuild: drop $(size_append) from cmd_zstd
  sh: rename suffix-y to suffix_y
  doc: kbuild: fix default in `imply` table
  microblaze: use built-in function to get CPU_{MAJOR,MINOR,REV}
  certs: move scripts/extract-cert to certs/
  kbuild: do not quote string values in include/config/auto.conf
  kbuild: do not include include/config/auto.conf from shell scripts
  certs: simplify $(srctree)/ handling and remove config_filename macro
  kbuild: stop using config_filename in scripts/Makefile.modsign
  certs: remove misleading comments about GCC PR
  certs: refactor file cleaning
  certs: remove unneeded -I$(srctree) option for system_certificates.o
  certs: unify duplicated cmd_extract_certs and improve the log
  certs: use $< and $@ to simplify the key generation rule
  kbuild: remove headers_check stub
  kbuild: move headers_check.pl to usr/include/
  certs: use if_changed to re-generate the key when the key type is changed
  ...

Makefile

@@ -1278,15 +1278,6 @@ headers: $(version_h) scripts_unifdef uapi-asm-generic archheaders archscripts
 	$(Q)$(MAKE) $(hdr-inst)=include/uapi
 	$(Q)$(MAKE) $(hdr-inst)=arch/$(SRCARCH)/include/uapi
 
-# Deprecated. It is no-op now.
-PHONY += headers_check
-headers_check:
-	@echo >&2 "=================== WARNING ==================="
-	@echo >&2 "Since Linux 5.5, 'make headers_check' is no-op,"
-	@echo >&2 "and will be removed after Linux 5.15 release."
-	@echo >&2 "Please remove headers_check from your scripts."
-	@echo >&2 "==============================================="
-
 ifdef CONFIG_HEADERS_INSTALL
 prepare: headers
 endif
@@ -1497,7 +1488,7 @@ MRPROPER_FILES += include/config include/generated          \
 		  debian snap tar-install \
 		  .config .config.old .version \
 		  Module.symvers \
-		  certs/signing_key.pem certs/signing_key.x509 \
+		  certs/signing_key.pem \
 		  certs/x509.genkey \
 		  vmlinux-gdb.py \
 		  *.spec
@@ -1723,9 +1714,9 @@ PHONY += prepare
 # now expand this into a simple variable to reduce the cost of shell evaluations
 prepare: CC_VERSION_TEXT := $(CC_VERSION_TEXT)
 prepare:
-	@if [ "$(CC_VERSION_TEXT)" != $(CONFIG_CC_VERSION_TEXT) ]; then \
+	@if [ "$(CC_VERSION_TEXT)" != "$(CONFIG_CC_VERSION_TEXT)" ]; then \
 		echo >&2 "warning: the compiler differs from the one used to build the kernel"; \
-		echo >&2 "  The kernel was built by: "$(CONFIG_CC_VERSION_TEXT); \
+		echo >&2 "  The kernel was built by: $(CONFIG_CC_VERSION_TEXT)"; \
 		echo >&2 "  You are using:           $(CC_VERSION_TEXT)"; \
 	fi