[gdb/testsuite] Use prototype to call libc functions

On openSUSE Tumbleweed (using glibc 2.36), I run into:
...
(gdb) print /d (int) munmap (4198400, 4096)^M
Invalid cast.^M
(gdb) FAIL: gdb.base/break-main-file-remove-fail.exp: cmdline: \
  get integer valueof "(int) munmap (4198400, 4096)"
...

The problem is that after starting the executable, the symbol has type
"void (*) (void)":
...
(gdb) p munmap
$1 = {<text variable, no debug info>} 0x401030 <munmap@plt>
(gdb) start
  ...
(gdb) p munmap
$2 = {void (void)} 0x7ffff7feb9a0 <__GI_munmap>
...
which causes the "Invalid cast" error.

Looking at the debug info for glibc for symbol __GI_munmap:
...
 <0><189683>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <189691>   DW_AT_name        : ../sysdeps/unix/syscall-template.S
    <189699>   DW_AT_producer    : GNU AS 2.39.0
<1><1896ae>: Abbrev Number: 2 (DW_TAG_subprogram)
    <1896af>   DW_AT_name        : __GI___munmap
    <1896b3>   DW_AT_external    : 1
    <1896b4>   DW_AT_low_pc      : 0x10cad0
    <1896bc>   DW_AT_high_pc     : 37
...
that's probably caused by this bit (or similar bits for other munmap aliases).

This is fixed in gas on trunk by commit 5578fbf672e ("GAS: Add a return type
tag to DWARF DIEs generated for function symbols").

Work around this (for say gas 2.39) by explicitly specifying the prototype for
munmap.

Likewise for getpid in a couple of other test-cases.

Tested on x86_64-linux.

gdb/testsuite/gdb.base/break-main-file-remove-fail.exp

@@ -87,7 +87,9 @@ proc test_remove_bp { initial_load } {
 	# should warn the user about it.
 	set pagesize [get_integer_valueof "pg_size" 0]
 	set align_addr [expr $bp_addr - $bp_addr % $pagesize]
-	set munmap [get_integer_valueof "(int) munmap ($align_addr, $pagesize)" -1]
+	set munmap_prototype "int (*) (void *, size_t)"
+	set munmap_expr "(($munmap_prototype) munmap) ($align_addr, $pagesize)"
+	set munmap [get_integer_valueof $munmap_expr -1]
 
 	if {$munmap != 0} {
 	    unsupported "can't munmap foo's page"

gdb/testsuite/gdb.base/dprintf-detach.exp

@@ -52,7 +52,7 @@ proc dprintf_detach_test { breakpoint_always_inserted dprintf_style disconnected
 	# Get PID of test program.
 	set inferior_pid -1
 	set test "get inferior process ID"
-	gdb_test_multiple "call (int) getpid ()" $test {
+	gdb_test_multiple "call ((int (*) (void)) getpid) ()" $test {
 	    -re ".* = ($decimal).*$gdb_prompt $" {
 		set inferior_pid $expect_out(1,string)
 		pass $test

gdb/testsuite/gdb.base/info-os.exp

@@ -39,7 +39,7 @@ if ![runto_main] then {
 # Get PID of test program.
 set inferior_pid ""
 set test "get inferior process ID"
-gdb_test_multiple "call (int) getpid()" $test {
+gdb_test_multiple "call ((int (*) (void)) getpid) ()" $test {
     -re ".* = ($decimal).*$gdb_prompt $" {
 	set inferior_pid $expect_out(1,string)
 	pass $test

gdb/testsuite/gdb.threads/siginfo-threads.exp

@@ -41,7 +41,7 @@ gdb_breakpoint [gdb_get_line_number "break-at-exit"]
 
 set test "get pid"
 set pid ""
-gdb_test_multiple "p (int) getpid ()" $test {
+gdb_test_multiple "p ((int (*) (void))getpid) ()" $test {
     -re " = (\[0-9\]+)\r\n$gdb_prompt $" {
 	set pid $expect_out(1,string)
 	pass $test