Fix #68: Use -O1 when compiling with gcc now

As reported gcc 8.1.1 can't produce a working lisp.  gcc 8.3.1 also
fails.  But as reported on cmucl-imp, 2019-04-08, by Juan Pablo Hierro
Alverez, -O1 works.

Use -O1.
2 jobs for issue-68-use-gcc-o1 in 18 minutes and 6 seconds (queued for 8 seconds)
latest
Status Job ID Name Coverage
  Test
passed #1535
linux
linux-runner

00:18:05

passed #1536
osx
osx-runner

00:10:33