lmathx missing nexttoward in cygwin

[David Manura <dm.lua@...>]

lmathx [1] fails compilation under Cygwin:

  lmathx.o:lmathx.c:(.text+0x85c): undefined reference to `_nexttoward'

Cygwin uses the newlib [2-3] C standard library, which lacks
nexttoward [4].  This is preventing LuaRocks and LuaDist from
installing lmathx cleanly under Cygwin.

The following patch will allow it to work:

--- lmathx.c~
+++ lmathx.c
@@ -186,11 +186,13 @@
   return 1;
 }

+#ifdef HAVE_NEXTTOWARD
 static int Lnexttoward(lua_State *L)
 {
   lua_pushnumber(L,nexttoward(A(1),A(2)));
   return 1;
 }
+#endif

 static int Lremainder(lua_State *L)
 {
@@ -263,7 +265,9 @@
        { "logb",       Llogb },
        { "nearbyint",  Lnearbyint },
        { "nextafter",  Lnextafter },
+#ifdef HAVE_NEXTTOWARD
        { "nexttoward", Lnexttoward },
+#endif
        { "remainder",  Lremainder },
        { "rint",       Lrint },
        { "round",      Lround },


BTW, it's not clear to me when nexttoward is useful over nextafter.
Moreover, nexttoward has a signature using "long double", but lmathx
treats double and long double both as a lua_Number.

[1] http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/#lmathx
[2] http://en.wikipedia.org/wiki/Newlib
[3] http://sourceware.org/newlib/libm.html
[4] http://www.cygwin.com/ml/cygwin/2009-07/msg00919.html