libstdc++: Use -fexcess-precision=standard for std::generate_canonical tests

On 32-bit x86 the default -fexcess-precision=fast setting used by
-std=gnu++20 results in unpredictable rounding which alters the number
of times that std::generate_canonical produces exactly 1.0f, which
means that the URBG is invoked a different number of times.

To ensure that the behaviour is consistent and the expected number of
calls happens, use -fexcess-precision=standard.

libstdc++-v3/ChangeLog:

	* testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc:
	Add -fexcess-precision=standard to options.
	* testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon.cc:
	Likewise.

Reviewed-by: Jakub Jelinek <[email protected]>

Author: jwakely

libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc

@@ -17,6 +17,7 @@
 
 // { dg-do run { target { c++11 && { ! simulator } } } }
 // { dg-require-cstdint "" }
+// { dg-additional-options -fexcess-precision=standard }
 
 #include <random>
 #include <testsuite_hooks.h>

libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/gencanon.cc

@@ -1,5 +1,6 @@
 // { dg-do run { target { c++11 && { ! simulator } } } }
 // { dg-skip-if "requires new impl" { *-*-* } { -D_GLIBCXX_USE_OLD_GENERATE_CANONICAL -D_GLIBCXX_USE_OLD_GENERATE_CANONICAL=1 } }
+// { dg-additional-options -fexcess-precision=standard }
 
 #include <random>
 #include <limits>