cmd/go: add 9g and 9l to documentation

Change-Id: I274c438ab168278dfbb34ada3ed9a7f7c66b66ef
Reviewed-on: https://go-review.googlesource.com/3834Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/go/build.go

@@ -81,14 +81,14 @@ and test commands:
 	-gccgoflags 'arg list'
 		arguments to pass on each gccgo compiler/linker invocation.
 	-gcflags 'arg list'
-		arguments to pass on each 5g, 6g, or 8g compiler invocation.
+		arguments to pass on each 5g, 6g, 8g, or 9g compiler invocation.
 	-installsuffix suffix
 		a suffix to use in the name of the package installation directory,
 		in order to keep output separate from default builds.
 		If using the -race flag, the install suffix is automatically set to race
 		or, if set explicitly, has _race appended to it.
 	-ldflags 'flag list'
-		arguments to pass on each 5l, 6l, or 8l linker invocation.
+		arguments to pass on each 5l, 6l, 8l, or 9l linker invocation.
 	-tags 'tag list'
 		a list of build tags to consider satisfied during the build.
 		For more information about build tags, see the description of

src/cmd/go/doc.go

@@ -100,14 +100,14 @@ and test commands:
 	-gccgoflags 'arg list'
 		arguments to pass on each gccgo compiler/linker invocation.
 	-gcflags 'arg list'
-		arguments to pass on each 5g, 6g, or 8g compiler invocation.
+		arguments to pass on each 5g, 6g, 8g, or 9g compiler invocation.
 	-installsuffix suffix
 		a suffix to use in the name of the package installation directory,
 		in order to keep output separate from default builds.
 		If using the -race flag, the install suffix is automatically set to race
 		or, if set explicitly, has _race appended to it.
 	-ldflags 'flag list'
-		arguments to pass on each 5l, 6l, or 8l linker invocation.
+		arguments to pass on each 5l, 6l, 8l, or 9l linker invocation.
 	-tags 'tag list'
 		a list of build tags to consider satisfied during the build.
 		For more information about build tags, see the description of