qemu: fix build for soft float targets

Soft float targets do no define the FE_... rounding constants
thus do not try to fesetround() in case the constants are not defined.

srcpkgs/qemu/patches/fix-softfloat-fesetround.patch

@@ -0,0 +1,39 @@
+Source: @pullmoll
+Upstream: no
+Reason: Target architectures with soft float do not define these constants.
+
+--- tests/fp/fp-bench.c	2020-12-08 17:59:44.000000000 +0100
++++ tests/fp/fp-bench.c	2020-12-12 20:38:40.702235420 +0100
+@@ -485,16 +485,32 @@
+ 
+     switch (rounding) {
+     case ROUND_EVEN:
++#if defined(FE_TONEAREST)
+         rhost = FE_TONEAREST;
++#else
++	return;
++#endif
+         break;
+     case ROUND_ZERO:
++#if defined(FE_TOWARDZERO)
+         rhost = FE_TOWARDZERO;
++#else
++	return;
++#endif
+         break;
+     case ROUND_DOWN:
++#if defined(FE_DOWNWARD)
+         rhost = FE_DOWNWARD;
++#else
++	return;
++#endif
+         break;
+     case ROUND_UP:
++#if defined(FE_UPWARD)
+         rhost = FE_UPWARD;
++#else
++	return;
++#endif
+         break;
+     case ROUND_TIEAWAY:
+         die_host_rounding(rounding);