d: __FUNCTION__ doesn't work in core.stdc.stdio functions without cast (PR101441)

d: __FUNCTION__ doesn't work in core.stdc.stdio functions without cast (PR101441)

Backports fix from upstream to allow __FUNCTION__ and
__PRETTY_FUNCTION__ to be used as C string literals.

Reviewed-on: https://github.com/dlang/dmd/pull/12923

	PR d/101441

gcc/d/ChangeLog:

	* dmd/expression.c (FuncInitExp::resolveLoc): Set type as `string'.
	(PrettyFuncInitExp::resolveLoc): Likewise.

gcc/testsuite/ChangeLog:

	* gdc.test/compilable/b19002.d: New test.

(cherry picked from commit 1a2306ffe79df89389cc850ce85c586d0f1c8264)