binutils/binutils: hide gold option if no support for current architecture

The gold linker does currently support only a limited set of architectures:
- x86 (32- and 64-bit)
- ARM

Hide the gold option for other architectures.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 148e80538623dd4fdb7895546138eabaf5712518)

 reporter_name="unknown"

 reporter_url="http://iphonelinux.org/index.php/Glibc_toolchain_using_crosstool-NG"

 reporter_comment="An (experimental) toolchain targeting the Apple's iPhone."