[gdb] Make make-init-c more robust

In commit 2711e4754fc ("Ensure cooked_index_entry self-tests are run"), we
rewrite the function definition of _initialize_dwarf2_entry into a normal
form that allows the make-init-c script to detect it:
...
 void _initialize_dwarf2_entry ();
-void _initialize_dwarf2_entry ()
+void
+_initialize_dwarf2_entry ()
...

Update make-init-c to also detect the "void _initialize_dwarf2_entry ()"
variant.

Tested on x86_64-linux, by reverting commit 2711e4754fc, rebuilding and
checking that build/gdb/init.c doesn't change.
1 file changed