[gdb/testsuite] Fix section matching in find_pc_sect_compunit_symtab

[gdb/testsuite] Fix section matching in find_pc_sect_compunit_symtab

When running test-case gdb.base/list-ambiguous.exp with target board readnow,
we run into:
...
FAIL: gdb.base/list-ambiguous.exp: list ambiguous_fun
...

The test-case contains two static functions ambiguous_fun, one in
list-ambiguous0.c and one in list-ambiguous1.c.

The list command is supposed to show both, but only the one from
list-ambiguous0.c is shown.

This is due to the section check in find_pc_sect_compunit_symtab.  It checks
whether the candidate compunit_symtab contains a symbol that has the required
section.  This check is only done for GLOBAL_BLOCK symbols.

The check succeeds for the compunit_symtab for list-ambiguous0.c, because it
contains main, but it fails for list-ambiguous0.c because it has no global
symbols.

Fix this by extending the section check to STATIC_BLOCK symbols.

Tested on x86_64-linux.

gdb/ChangeLog:

2020-10-27  Tom de Vries  <tdevries@suse.de>

	* symtab.c (find_pc_sect_compunit_symtab): Include STATIC_BLOCK
	symbols in section check.

gdb/testsuite/ChangeLog:

2020-10-27  Tom de Vries  <tdevries@suse.de>

	* gdb.base/list-ambiguous-readnow.exp: New file.