Currently the jit requires you to specify --enable-host-shared, or the
build eventually fails with linker errors (this is something of a FAQ
for people trying out the jit).
We seem to have two choices here:
(A) default to --enable-host-shared when jit is an enabled language
(B) have the toplevel configure reject jit as language if
--enable-host-shared is not supplied.
FWIW apparently Darwin defaults to position-independent code, so it's not
explicitly needed there.
I think (B) is the better option for us, since there is a performance
cost: there are people who perform benchmarking of GCC (and publish
their results on prominent websites). If they turn on the jit and use
the same configuration to do their benchmarking of the rest of GCC,
they'll see GCC 5 be apparently slower than earlier releases. This
is sufficiently subtle that I don't think it's reasonable to simply
document it and expect 3rd-party reviewers to see such a note in the
documentation before benchmarking.
The attached patch implements (B), with a note in the error message
recommending that people configure and build GCC twice to avoid the
performance hit, so that it can be self-documenting.
Tested by hand with various combinations of values for
--enable-host-shared and --enable-languages.
OK for stage 4?
PR jit/64780
* configure.ac: Require the user to explicitly specify
--enable-host-shared if the jit is enabled.
* configure: Regenerate.