cmd/go: make it clearer that go generate accepts all build flags

Just add one word to clarify that -n -v -x are not the only build flags supported.

Fixes #13237.

Change-Id: I880472639bf2fc1a0751a83041bc7ddd0c9e55f4
Reviewed-on: https://go-review.googlesource.com/17062
Reviewed-by: Andrew Gerrand <[email protected]>

Author: robpike

src/cmd/go/alldocs.go

@@ -451,7 +451,7 @@ Go generate accepts one specific flag:
 		any trailing spaces and final newline) matches the
 		expression.
 
-It also accepts the standard build flags -v, -n, and -x.
+It also accepts the standard build flags including -v, -n, and -x.
 The -v flag prints the names of packages and files as they are
 processed.
 The -n flag prints commands that would be executed.

src/cmd/go/generate.go

@@ -115,7 +115,7 @@ Go generate accepts one specific flag:
 		any trailing spaces and final newline) matches the
 		expression.
 
-It also accepts the standard build flags -v, -n, and -x.
+It also accepts the standard build flags including -v, -n, and -x.
 The -v flag prints the names of packages and files as they are
 processed.
 The -n flag prints commands that would be executed.