Add musl fenv.c needed by musl math functions.

system/lib/libc.symbols

@@ -46,6 +46,13 @@
          T expm1
          T expm1f
          T expm1l
+         T feclearexcept
+         T feraiseexcept
+         T fetestexcept
+         T fegetround
+         T __fesetround
+         T fegetenv
+         T fesetenv
          T fdim
          T fdimf
          T fdiml

system/lib/libc/musl/src/fenv/fenv.c

@@ -0,0 +1,38 @@
+#include <fenv.h>
+
+/* Dummy functions for archs lacking fenv implementation */
+
+int feclearexcept(int mask)
+{
+	return 0;
+}
+
+int feraiseexcept(int mask)
+{
+	return 0;
+}
+
+int fetestexcept(int mask)
+{
+	return 0;
+}
+
+int fegetround(void)
+{
+	return FE_TONEAREST;
+}
+
+int __fesetround(int r)
+{
+	return 0;
+}
+
+int fegetenv(fenv_t *envp)
+{
+	return 0;
+}
+
+int fesetenv(const fenv_t *envp)
+{
+	return 0;
+}

tools/system_libs.py

@@ -98,6 +98,9 @@ def create_libc():
        'isxdigit.c',
        'tolower.c',
       ]],
+      ['fenv', [
+        'fenv.c'
+      ]],
       ['internal', [
        'intscan.c',
        'floatscan.c',