Replace int with bool in solib.c

Replace int with bool in solib.c

This does not touch "int from_tty" and a couple of other instances
that require a bigger change.

gdb/ChangeLog:

2019-11-25  Christian Biesinger  <cbiesinger@google.com>

	* solib.c (solib_find_1): Change int to bool.
	(exec_file_find): Change int to bool.
	(solib_find): Change int to bool.
	(solib_read_symbols): Change int to bool.
	(solib_used): Change int to bool.
	(solib_add): Change int to bool.
	(info_sharedlibrary_command): Change int to bool.
	(solib_contains_address_p): Change int to bool.
	(solib_keep_data_in_core): Change int to bool.
	(in_solib_dynsym_resolve_code): Change int to bool.
	(reload_shared_libraries_1): Change int to bool.
	(gdb_sysroot_changed): Change int to bool.
	* solib.h (solib_read_symbols): Change int to bool.
	(solib_contains_address_p): Change int to bool.
	(solib_keep_data_in_core): Change int to bool.
	(in_solib_dynsym_resolve_code): Change int to bool.
	(libpthread_name_p): Change int to bool.

Change-Id: Id695ed4ed0c3526af477d4d2bf585a7193c36cab