compiler: enable CONFIG_OPTIMIZE_INLINING forcibly

Commit 9012d01166 ("compiler: allow all arches to enable
CONFIG_OPTIMIZE_INLINING") allowed all architectures to enable this
option.  A couple of build errors were reported by randconfig, but all of
them have been ironed out.

Towards the goal of removing CONFIG_OPTIMIZE_INLINING entirely (and it
will simplify the 'inline' macro in compiler_types.h), this commit changes
it to always-on option.  Going forward, the compiler will always be
allowed to not inline functions marked 'inline'.

This is not a problem for x86 since it has been long used by
arch/x86/configs/{x86_64,i386}_defconfig.

I am keeping the config option just in case any problem crops up for other
architectures.

The code clean-up will be done after confirming this is solid.

Link: http://lkml.kernel.org/r/20190830034304.24259-1-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -311,7 +311,7 @@ config HEADERS_CHECK
 	  relevant for userspace, say 'Y'.
 
 config OPTIMIZE_INLINING
-	bool "Allow compiler to uninline functions marked 'inline'"
+	def_bool y
 	help
 	  This option determines if the kernel forces gcc to inline the functions
 	  developers have marked 'inline'. Doing so takes away freedom from gcc to
@@ -322,8 +322,6 @@ config OPTIMIZE_INLINING
 	  decision will become the default in the future. Until then this option
 	  is there to test gcc for this.
 
-	  If unsure, say N.
-
 config DEBUG_SECTION_MISMATCH
 	bool "Enable full Section mismatch analysis"
 	help