[libstdc++] Fix PR libstdc++/3988, typo in libmath/stubs.c

[Peter Schmid]

I fixed the PR libstdc++/3988, a gcc 3.0.1 regression with respect to
gcc 3.0. The name of the guard was wrong. After replacing the name
_GBLICPP_HAVE_LOGL with HAVE_LOGL the test case passes. The logl
function from glibc is now used rather than the function defined in 
the stubs.c file.  After applying the appended patch, all tests from the boost
regression test suite pass on the i686-pc-linux-gnu target! 

Please apply this patch to the branch and the main line, if OK.

Hope this helps,

Peter Schmid

Output of the testcase t include in PR 3988

./t
0       1
0       1
 

2001-08-14  Peter Schmid  <schmid@snake.iap.physik.tu-darmstadt.de>

        * libstdc++-v3/libmath/stubs.c: Fix PR/3988, replace
          _GBLICPP_HAVE_LOGL with HAVE_LOGL


*** libstdc++-v3/libmath/stubs.c.orig	Tue Aug 14 01:13:03 2001
--- libstdc++-v3/libmath/stubs.c	Tue Aug 14 01:13:31 2001
*************** logf(float x)
*** 143,149 ****
  }
  #endif
  
! #ifndef _GBLICPP_HAVE_LOGL
  long double
  logl(long double x)
  {
--- 143,149 ----
  }
  #endif
  
! #ifndef HAVE_LOGL
  long double
  logl(long double x)
  {