Add a flag -fgo-debug-escape-hash for debugging escape analysis.
    It takes a binary string, optionally led by a "-", as argument.
    When specified, the escape analysis runs only on functions whose
    name is hashed to a value with matching suffix. The "-" sign
    negates the match, i.e. the analysis runs only on functions with
    non-matching hash.

    Reviewed-on: https://go-review.googlesource.com/83878

	* lang.opt (fgo-debug-escape-hash): New option.
	* go-c.h (struct go_create_gogo_args): Add debug_escape_hash
	field.
	* go-lang.c (go_langhook_init): Set debug_escape_hash field.
	* gccgo.texi (Invoking gccgo): Document -fgo-debug-escape-hash.

From-SVN: r256393