Description of problem:

There is HAVE_FAST_COMPILER check in flint source. But it checks for clang or gcc 4.7.3+ in a way that gcc 5.x.y is not good enough one.

// Whether or not the compiler is good enough to compile all of t-mpz.cpp
// in reasonable time and space.
#ifndef HAVE_FAST_COMPILER
#ifdef __clang__
// clang 3.4 works; let's suppose all work until someone complains
#define HAVE_FAST_COMPILER 1
#elif defined(__GNUC__)
// gcc 4.7.3 is good enough, supposedly all higher ones are too
#define HAVE_FAST_COMPILER \
    (__GNUC__ >= 4 && \
         ((__GNUC_MINOR__ == 7 && __GNUC_PATCHLEVEL__ >= 3) \
          || (__GNUC_MINOR__ > 7)))
#else
#define HAVE_FAST_COMPILER 0
#endif
#endif

Some tests are not run without fast compiler, code also differ in both situations.

Version-Release number of selected component (if applicable):

2.5.2-1

How reproducible:

always

Steps to Reproduce:
1. do a build

Actual results:

HAVE_FAST_COMPILER=0

Expected results:

HAVE_FAST_COMPILER=1

Additional info: