BUILD: Makefile: speed up compiler options detection

BUILD: Makefile: speed up compiler options detection

Commits b78016649 and d3a7f4035 brought the ability to detect the build
options and warnings that the compiler supports. However, they're detected
using "$(CC) -c", which is 50% slower than "$(CC) -E" for the same result,
just because it starts the assembler at the end. Given that we're starting
to check for a number of warnings, this detection alone starts to become
visible, taking a bit more than 300 ms on the build time. Let's switch to
-E instead to shrink this incompressible time by roughly 100 ms.