kbuild: introduce ld-option

ld-option is used to check if $(LD) supports a specific option.

Based on patch from Andi Kleen.

Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
First use is to check if option -X is supported (upcoming patch).
Theis is ne
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 7847fce..71c602d 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -18,6 +18,7 @@
 	   --- 3.9 Dependency tracking
 	   --- 3.10 Special Rules
 	   --- 3.11 $(CC) support functions
+	   --- 3.12 $(LD) support functions
 
 	=== 4 Host Program support
 	   --- 4.1 Simple Host Program
@@ -570,6 +571,19 @@
 			endif
 		endif
 
+--- 3.12 $(LD) support functions
+
+    ld-option
+	ld-option is used to check if $(LD) supports the supplied option.
+	ld-option takes two options as arguments.
+	The second argument is an optional option that can be used if the
+	first option is not supported by $(LD).
+
+	Example:
+		#Makefile
+		LDFLAGS_vmlinux += $(call really-ld-option, -X)
+
+
 === 4 Host Program support
 
 Kbuild supports building executables on the host for use during the