A feature of gcc on Intel platforms is to enable the FTZ and DAZ
features available on modern Intel CPUs. Those features convert
denormal floating point values to zero to avoid expensive and slow
exception handling inside the CPU. Details can be found at
https://www.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/floating-point-operations/set-the-ftz-and-daz-flags.html
Some Linux distributions now started to make this flag the compiler
default and build the standard runtime libraries with this switch
turned on. On those systems the definition of least-*-*-float evaluates
to zero, no longer adhering to their specification, and as such failing
test cases relying on them. Compiling sbcl with this compiler feature
explicitly turned off is not preventing this problem from happening
since we use functions from libm that is built with this switch turned
on and as such will apply the conversions nevertheless to our surprise.
Therefore this introduces a new feature "normalize-float" for systems
with that behavior. This automatically gets switched on by an automated
test. The test is designed to detect similar behavior also on non-Intel
systems. The definitions of least-*-*-float are adapted accordingly.
Updated the patch to fix the problem instead of just mark the tests as expected failure.