Fix deadlock when the compiler crashes internally

[connorjward]

Changes

• Prevent compiler errors from causing a deadlock
• Print out compiler errors when running CI as the log files aren't available
• Disable -ffast-math for GCC to fix internal compiler error on CI runners
• Re-enable skipped IO tests

Closes #4819

What happened

In #4911 I have been investigating a very tricky timeout bug. I finally tracked it down to the following compiler error:

during GIMPLE pass: slp
mfe.c: In function 'expression_kernel':
mfe.c:8:13: internal compiler error: Floating point exception
    8 | static void expression_kernel(double complex *__restrict__ A, double complex const *__restrict__ w_0, double complex const *__restrict__ w_1)
      |             ^~~~~~~~~~~~~~~~~
0x108d932 internal_error(char const*, ...)
        ???:0
0x172411d vect_slp_analyze_operations(vec_info*)
        ???:0
0x13f916a vect_slp_function(function*)
        ???:0

This would only happen on the CI runners. On my workstation with the same Docker image things ran fine. Disabling fast math fixes it.