ACPICA: gcc-specific: Fix possible issue with the strchr function.

Some versions of gcc implement strchr via a macro, which either
contains bugs or can provoke a bug in the compiler. This change
fixes a possible compile-time error when using this function.
The problem is usually seen when compiling the getopt.c module.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>