GNU libc 2.31 compatibility

Optimized builds of Ardour use various _finite math methods
(due to -ffast-math). Those functions have apparently been
removed, and replaced with macros and are no longer available
in libm/libc++.

see also
https://discourse.ardour.org/t/a-eq-and-a-comp-fail-on-manjaro-xfce/103122
https://lists.gnu.org/archive/html/info-gnu/2020-02/msg00001.html

wscript

@@ -59,7 +59,7 @@ compiler_flags_dictionaries= {
         # Flags to use posix pipes between compiler stages
         'pipe' : '-pipe',
         # Flags for maximally optimized build
-        'full-optimization' : [ '-O3', '-fomit-frame-pointer', '-ffast-math', '-fstrength-reduce', ],
+        'full-optimization' : [ '-O3', '-fomit-frame-pointer', '-ffast-math', '-fstrength-reduce', '-fno-finite-math-only' ],
         # Flag to ensure that compiler error output includes column/line numbers
         'show-column' : '-fshow-column',
         # Flags required to build for x86 only (OS X feature)