Complete the previous commit (block_found refactoring)

Complete the previous commit (block_found refactoring)

The previous commit (Replace the block_found global with explicit
data-flow) lacks updates in a couple of files because it was not
tested building GDB with --enable-targets=all... but buildbots did.
This adds the appropriate simple updates to fix the build.

gdb/ChangeLog:

	* alpha-mdebug-tdep.c (find_proc_desc): Update call to
	lookup_symbol.
	* ft32-tdep.c (ft32_skip_prologue): Likewise.
	* moxie-tdep.c (moxie_skip_prologue): Likewise.
	* mt-tdep.c (mt_skip_prologue): Likewise.
	* xstormy16-tdep.c (xstormy16_skip_prologue): Likewise.