class/c: Default to using gcc -E for running preprocessor
class/c: Default to using gcc -E for running preprocessor

The result should be the same, and at least eglibc configure script is looking
for CPP being something like this.  So this fixes eglibc configure and
possibly others.

Signed-off-by: Esben Haabendal <c5ba3f1141bb30a64dd6c7e6726a53a85adc9442@prevas.dk>

sknsean/core,sknsean/core,hundeboll/core,sknsean/core,hundeboll/core,sknsean/core,hundeboll/core,diorcety/oe-lite-core,sknsean/core,diorcety/oe-lite-core,hundeboll/core