We can't assign to *stdout and *stderr with musl libc
because both file pointers are const.

--- a/src/main.cc	2014-12-19 22:24:38.000000000 +0100
+++ b/src/main.cc	2015-11-19 13:53:23.419299858 +0100
@@ -301,21 +301,25 @@
     if (ap.redirect) {
         FILE *newfp;
         newfp = std::freopen((userStdPath + "/Output.log").c_str(), "w", stdout);
+#if defined(__GLIBC__)
         if ( newfp == NULL ) {  // This happens on NT
             newfp = fopen((userStdPath + "/Output.log").c_str(), "w");
             if (newfp) {  // in case stdout is a macro
                 *stdout = *newfp;
             }
         }
+#endif
         setvbuf(stdout, NULL, _IOLBF, BUFSIZ);   // Line buffered
 
         newfp = std::freopen((userStdPath + "/Error.log").c_str(), "w", stderr);
+#if defined(__GLIBC__)
         if ( newfp == NULL ) {  // This happens on NT
             newfp = fopen((userStdPath + "/Error.log").c_str(), "w");
             if (newfp) {  // in case stderr is a macro
                 *stderr = *newfp;
             }
         }
+#endif
         setbuf(stderr, NULL);   // No buffering
     }