gdb, testsuite: Adapt gdb.base/callfuncs.exp for new clang warning.

gdb, testsuite: Adapt gdb.base/callfuncs.exp for new clang warning.

Clang 15.0.0 enabled the warning for deprecated non-prototype functions
by default: https://reviews.llvm.org/D122895
Callfuncs.exp is impacted and won't run due to new warnings:

callfuncs.c:339:5: warning: a function declaration without a prototype is
deprecated in all versions of C and is not supported in C2x
[-Wdeprecated-non-prototype]
int t_float_values (float_arg1, float_arg2)

This patch disables those warnings with -Wno-deprecated-non-prototype.
Removing the test for deprecated syntax would also be an option. But I will
leave that up for others to decide/implement.