3.99.91
[SV 39934] Verify jobserver FDs before something else uses them.
Expand the loadable object support.
[SV 27374] Fatal immediately on unrecoverable fopen() errors.
[SV 39203] Don't set MAKEFLAGS when restarting.
When .POSIX: is specified use POSIX-standard macro values by default.
Enhance the output sync mode.
Update the test template. A few fixes in run_make_test(). Rename implicit_prereq_eval to patternrules, to be the start of a suite of tests of pattern rules.