Compiler not detecting unused functions

I recently inherited a project and I am trying to clean it up. I have the following warnings enabled but I don't think the unused functions are being detected or at least reported by the compiler.

-Wall -Wunused -Wunused-function -Wextra

Here's a the build command for one of the source files

nios2-elf-gcc -xc -MP -MMD -c -I../gsi_proc_bsp//HAL/inc -I../gsi_proc_bsp/ -I../gsi_proc_bsp//drivers/inc -DSYSTEM_BUS_WIDTH=32 -pipe -D__hal__ -DALT_NO_C_PLUS_PLUS -DALT_NO_CLEAN_EXIT -D'exit(a)=_exit(a)' -DALT_NO_EXIT -DALT_NO_INSTRUCTION_EMULATION -DALT_STACK_CHECK -fstack-check -DALT_SINGLE_THREADED -DALTERA_AVALON_UART_USE_IOCTL -O1 -g -Wall -Wunused -Wunused-function -Wextra -mhw-div -mcustom-fpu-cfg=60-1 -mhw-mul -mno-hw-mulx -o obj/default/.metadata/.plugins/org.eclipse.cdt.make.core/specs.o .metadata/.plugins/org.eclipse.cdt.make.core/specs.c

I just to test the compiler flag I added the following function, and the compiler detects the unused variable, but not the unused function!

void MyUnusedFunction(void)
{
    int i;
    printf("I do nothing\n");
}

Any ideas?