kconfig: add basic helper macros to scripts/Kconfig.include

Kconfig got text processing tools like we see in Make.  Add Kconfig
helper macros to scripts/Kconfig.include like we collect Makefile
macros in scripts/Kbuild.include.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>
diff --git a/Kconfig b/Kconfig
index 5b55d87..a90d9f9 100644
--- a/Kconfig
+++ b/Kconfig
@@ -7,4 +7,6 @@
 
 comment "Compiler: $(CC_VERSION_TEXT)"
 
+source "scripts/Kconfig.include"
+
 source "arch/$(SRCARCH)/Kconfig"
diff --git a/MAINTAINERS b/MAINTAINERS
index b87723a..79decb1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7639,6 +7639,7 @@
 S:	Maintained
 F:	Documentation/kbuild/kconfig*
 F:	scripts/kconfig/
+F:	scripts/Kconfig.include
 
 KDUMP
 M:	Dave Young <dyoung@redhat.com>
diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index a992f8e..9d529f2 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -3,6 +3,8 @@
 
 comment "Compiler: $(CC_VERSION_TEXT)"
 
+source "scripts/Kconfig.include"
+
 source "arch/um/Kconfig.common"
 
 menu "UML-specific options"
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
new file mode 100644
index 0000000..bf7c0c9
--- /dev/null
+++ b/scripts/Kconfig.include
@@ -0,0 +1,27 @@
+# Kconfig helper macros
+
+# Convenient variables
+comma       := ,
+quote       := "
+squote      := '
+empty       :=
+space       := $(empty) $(empty)
+dollar      := $
+right_paren := )
+left_paren  := (
+
+# $(if-success,<command>,<then>,<else>)
+# Return <then> if <command> exits with 0, <else> otherwise.
+if-success = $(shell,{ $(1); } >/dev/null 2>&1 && echo "$(2)" || echo "$(3)")
+
+# $(success,<command>)
+# Return y if <command> exits with 0, n otherwise
+success = $(if-success,$(1),y,n)
+
+# $(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)
+
+# $(ld-option,<flag>)
+# Return y if the linker supports <flag>, n otherwise
+ld-option = $(success,$(LD) -v $(1))