libm/riscv: Use common fma code when necessary

For RISC-V targets without hardware FMA support, include the
common fma implementation to provide that API.

Signed-off-by: Keith Packard <keithp@keithp.com>

newlib/libm/machine/riscv/s_fma.c

@@ -46,4 +46,6 @@ fma (double x, double y, double z)
 	return result;
 }
 
+#else
+#include "../../common/s_fma.c"
 #endif

newlib/libm/machine/riscv/sf_fma.c

@@ -46,4 +46,6 @@ fmaf (float x, float y, float z)
 	return result;
 }
 
+#else
+#include "../../common/sf_fma.c"
 #endif