Fix spurious define in openblas_config.h

TARGET as specified with make is already return-terminated when getarch reads it. This led to an empty line written to config_last.h that awk in Makefile.install then expanded to a spurious "#define OPENBLAS_" in openblas_config.h (as noted by "kmb" on the mailing list)

getarch.c

@@ -1098,6 +1098,7 @@ int main(int argc, char *argv[]){
 	      p ++;
 	    }
 	  } else {
+	    if (*p != '\n')
 	    printf("%c", *p);
 	    p ++;
 	  }