RFR: JDK-8217723 Switch ld from bfd to gold on gcc toolchain

[Florian Weimer]

* Magnus Ihse Bursie:

> The default binutils linker used by gcc, the bfd linker, is slow. The
> new replacement, gold, has been distributed alongside gcc for several
> years now, and is a well mature, and much faster, replacement.

The gold linker is an optional component of binutils, not available in
all builds.  For example, binutils in Red Hat Enterprise Linux 7.6 does
not include gold on the ppc64le architecture.

The gold linker also supports a different set of features compared to
BFD ld, which may or may not be what you want.  But I think OpenJDK does
not use many tricky ELF features, so the differences probably do not
matter.

Is it possible to add -fuse-ld=gold to LDFLAGS externally, outside the
build system, so that the build system can use the gold linker if people
prefer it over BFD ld?

Or you could configure your binutils with --enable-gold=default, so that
it defaults to ld.gold, again not requiring any OpenJDK changes.

Thanks,
Florian