Fix PR target/107248

Fix PR target/107248

This is the infamous PR rtl-optimization/38644 rearing its ugly head for
leaf functions on SPARC more than a decade later...  Richard E.'s generic
solution has never been implemented so let's do as other RISC back-ends did.

gcc/
	PR target/107248
	* config/sparc/sparc.cc (sparc_expand_prologue): Emit a frame
	blockage for leaf functions.
	(sparc_flat_expand_prologue): Emit frame instead of full blockage.
	(sparc_expand_epilogue): Emit a frame blockage for leaf functions.
	(sparc_flat_expand_epilogue): Emit frame instead of full blockage.