This patch to the gccgo manual documents the new options and compiler
directives.  It also updates the section on function names to suggest
-fgo-pkgpath rather than -fgo-prefix; -fgo-prefix still works, but
-fgo-pkgpath is preferred.  Bootstrapped on x86_64-pc-linux-gnu.
Committed to mainline.

Ian

2016-08-09  Ian Lance Taylor  <iant@google.com>

* gccgo.texi (Invoking gccgo): Document -fgo-optimize-allocs and
-fgo-debug-escae.
(Compiler Directives): New chapter.
(Function Names): Describe using //go:linkname.  Suggest using
-fgo-pkgpath rather than -fgo-prefix.