[main] use <gnu/lib-names.h> for resolving -lm on linux machines

As suggested by @cjwelborn in #16 the above header defines LIBM_SO which is what
we should be using when opening -lm.

Fixes: #17

src/main.c

@@ -11,6 +11,10 @@
 #include "gc.h"
 #include "preprocess.h"
 
+#if defined(BUILD_LINUX)
+ #include <gnu/lib-names.h>
+#endif
+
 extern FILE* cfilein;
 extern int cfileparse();
 
@@ -77,6 +81,11 @@ static int open_library(char *libname)
     char *tmp, *full_library_name;
     int ret;
 
+#if defined(BUILD_LINUX)
+    if (!strcmp(libname, "m"))
+        libname = LIBM_SO;
+#endif
+
     /* First, attempt to open just the library, if it has been fully
      * specified. */
     if (dlopen(libname, RTLD_NOW | RTLD_GLOBAL))