cmake: zephyr_cc_option(-fmacro-prefix-map=${ZEPHYR_BASE}=.)

If the compiler supports it, strip the ${ZEPHYR_BASE} prefix from the
__FILE__ macro used in __ASSERT* macros, in the
.noinit."/home/joe/zephyr/fu/bar.c" section names and in any application
code. This saves some memory, stops leaking user locations in binaries,
makes failure logs more deterministic and most importantly makes builds
more deterministic.

- .noinit section names now look like this in objdump -h:

 17 .noinit."./kernel/init.c".2 00001100  00000000  ...

 18 .noinit."./kernel/init.c".1 00001200  00000000  ...

 19 .noinit."./kernel/init.c".3 00001800  00000000  ...

- The output of __ASSERT* macros now looks like this:

  ASSERTION FAIL [0] @ ./samples/hello_world/src/main.c:13
    The world comes crashing down
  ***** Kernel Panic! *****
  Current thread ID = 0x00400040

Signed-off-by: Marc Herbert <marc.herbert@intel.com>