[gdb/symtab] Fix disassembly of non-contiguous functions

[gdb/symtab] Fix disassembly of non-contiguous functions

When running test-case gdb.dwarf2/dw2-ranges-func.exp with target board
readnow, we have:
...
FAIL: gdb.dwarf2/dw2-ranges-func.exp: disassemble foo (pattern 2)
...

The function foo consists of two ranges:
...
 <1><12f>: Abbrev Number: 7 (DW_TAG_subprogram)
    <130>   DW_AT_external    : 1
    <131>   DW_AT_name        : foo
    <135>   DW_AT_ranges      : 0x40
...
which are listed here:
...
    00000040 00000000004004c1 00000000004004dc
    00000040 00000000004004ae 00000000004004ba
...

Normally the disassemble instruction lists both ranges, but with -readnow it
only lists the first.

This is due to function find_pc_partial_function, which only interacts with
partial symtabs, but not with expanded ones.

Fix this by using find_pc_sect_compunit_symtab in find_pc_partial_function.

Tested on x86_64, with native and target board readnow.

This fixes 19 FAILs for target board readnow, in test-cases
gdb.arch/amd64-entry-value.exp, gdb.base/multi-forks.exp,
gdb.dwarf2/dw2-ranges-func.exp and gdb.linespec/skip-two.exp.

gdb/ChangeLog:

2020-04-23  Tom de Vries  <tdevries@suse.de>

	* blockframe.c (find_pc_partial_function): Use
	find_pc_sect_compunit_symtab rather than
	objfile->sf->qf->find_pc_sect_compunit_symtab.