[gdb/testsuite] Fix gdb.python/py-objfile.exp with gcc 15

When running test-case gdb.python/py-objfile.exp with gcc 15, we get:
...
(gdb) p main^M
$2 = {int (void)} 0x40066c <main>^M
(gdb) FAIL: $exp: print main with debug info
...

The source file declares main as "int main ()"
...
and until C23 this meant a non-prototype function declaration and we'd have:
...
(gdb) p main^M
$2 = {int ()} 0x40066c <main>^M
...

However, starting C23 "int main ()" is simply equivalent to "int main (void)".

Fix this by:
- declaring main as "int main (void)" in the test-case, and
- updating the regexp to expect an "int (void)" prototype.

Likewise in gdb.base/jit-bfd-name.exp.

Tested on aarch64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

PR testsuite/32756
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32756

gdb/testsuite/gdb.base/jit-bfd-name.exp

@@ -67,11 +67,13 @@ gdb_breakpoint [gdb_get_line_number "break here 1" $::main_srcfile]
 gdb_continue_to_breakpoint "break here 1"
 
 # Confirm that the two expected functions are available.
+set re_f1 [string_to_regexp "int jit_function_0001(void)"]
+set re_f2 [string_to_regexp "int jit_function_0002(void)"]
 gdb_test "info function ^jit_function" \
     [multi_line \
 	 "File \[^\r\n\]+jit-elf-solib.c:" \
-	 "${decimal}:\\s+int jit_function_0001\\(\\);" \
-	 "${decimal}:\\s+int jit_function_0002\\(\\);"]
+	 "${decimal}:\\s+$re_f1;" \
+	 "${decimal}:\\s+$re_f2;"]
 
 # Capture the addresses of each JIT symfile.
 set symfile_addrs {}

gdb/testsuite/gdb.base/jit-elf-solib.c

@@ -22,4 +22,4 @@
 #error "Must define the FUNCTION_NAME macro to set a jited function name"
 #endif
 
-int FUNCTION_NAME() { return 42; }
+int FUNCTION_NAME(void) { return 42; }

gdb/testsuite/gdb.python/py-objfile.c

@@ -19,7 +19,7 @@ int global_var = 42;
 static int __attribute__ ((used)) static_var = 50;
 
 int
-main ()
+main (void)
 {
   int some_var = 0;
   return 0;

gdb/testsuite/gdb.python/py-objfile.exp

@@ -144,7 +144,8 @@ gdb_test "python print (sep_objfile.owner.filename)" "${testfile}2" \
 gdb_test "python print (sep_objfile.owner.username)" "${testfile}2" \
     "Test user-name of owner of separate debug file"
 
-gdb_test "p main" "= {int \\(\\)} $hex <main>" \
+set re_prototype [string_to_regexp "int (void)"]
+gdb_test "p main" "= {$re_prototype} $hex <main>" \
     "print main with debug info"
 
 # Separate debug files are not findable.