[libc++] tests with picolibc: mark fenv tests as unsupported (llvm#74610)

The FE_* macros checked for in cfenv.pass.cpp are not required to be
defined, if the relevant options are _not_ available. Picolibc happens
not to provide these on some platforms.

Author: domin144

libcxx/test/std/depr/depr.c.headers/fenv_h.compile.pass.cpp

@@ -6,8 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Floating point exceptions are required for the FE_... macros to be defined.
-// XFAIL: LIBCXX-PICOLIBC-FIXME
+// Picolibc does not define some of the floating point environment macros for
+// arm platforms without hardware floating point support.
+// UNSUPPORTED: LIBCXX-PICOLIBC-FIXME
 
 // <fenv.h>
 

libcxx/test/std/numerics/cfenv/cfenv.syn/cfenv.pass.cpp

@@ -6,8 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Floating point exceptions are required for the FE_... macros to be defined.
-// XFAIL: LIBCXX-PICOLIBC-FIXME
+// Picolibc does not define some of the floating point environment macros for
+// arm platforms without hardware floating point support.
+// UNSUPPORTED: LIBCXX-PICOLIBC-FIXME
 
 // <cfenv>