bootstrap: try better workaround for builds on Linux/HPPA

The workaround currently present works fine without -O or with -O1, but fails
with -Os or -O2 and higher. Using -O2 is common e.g. in Gentoo, as resulting in
bugs like this:

https://bugs.gentoo.org/473276

Prevent the workaround for higher optimization levels to make bootstrapping
more likely to succeed.

This is still a workaround as ld still keeps crashing in some situations.
Merge topic 'hppa-bootstrap'

ca63bb1 bootstrap: try better workaround for builds on Linux/HPPA