Reduce gcc/Makefile prints to simplify build output

[jjcarstens]

The gcc commandlines and other prints can be useful, but most of the
time they are overwhelming especially for non-C programmers. This
simplifies the prints.

To re-enable, set V=1 like is common with many Makefile/C projects.
For example V=1 make, V=1 mix compile, etc.

Example output:

> exqlite √ % mix test                                                                                                                                                                                          makefile
 CC sqlite3.o
 LD sqlite3_nif.so
..........................................................

Finished in 0.4 seconds (0.00s async, 0.4s sync)
58 tests, 0 failures

Randomized with seed 523581