compiler: turn on escape analysis by default

compiler: turn on escape analysis by default

    The escape analysis now runs by default. It can be disabled with
    the negative flag, -fno-go-optimize-allocs.

    Reviewed-on: https://go-review.googlesource.com/86247

	* lang.opt (fgo-optimize): Remove RejectNegative.
	* go-c.h (go_enable_optimize): Update declaration to take value
	argument.
	* go-lang.c (go_langhook_handle_option): Pass value to
	go_enable_optimize.
	* gccgo.texi (Invoking gccgo): Update -fgo-optimize-allocs doc.

From-SVN: r257319