configure.ac: fix libm checks (Trac #3730)

libbfd pulled libm as dependency and broke LIBM= detection.

Patch moves libm in library tests as early as possible.
Thanks to asuffield for suggesting such a simple fix.
Thanks to Roie Kerstein and Renato Gallo for finding
and tracking down the issue.

diff --git a/configure.ac b/configure.ac
index fa5f9a3..15b3c85 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -723,18 +723,22 @@ if test $HaveLibMingwEx = YES ; then
   AC_DEFINE([HAVE_MINGWEX], [1], [Define to 1 if you have the mingwex library.])
 fi
 
-dnl ** check whether this machine has BFD and liberty installed (used for debugging)
-dnl    the order of these tests matters: bfd needs liberty
-AC_CHECK_LIB(iberty, xmalloc)
-AC_CHECK_LIB(bfd,    bfd_init)
-
 dnl ** check for math library
+dnl    Keep that check as early as possible.
+dnl    as we need to know whether we need libm
+dnl    for math functions or not
+dnl    (see http://hackage.haskell.org/trac/ghc/ticket/3730)
 AC_CHECK_FUNC(atan,[fp_libm_not_needed=yes;LIBM=],[fp_libm_not_needed=dunno])
 if test x"$fp_libm_not_needed" = xdunno; then
    AC_CHECK_LIB([m], [atan], [LIBS="-lm $LIBS"; LIBM="-lm"],[LIBM=])
 fi
 AC_SUBST([LIBM])
 
+dnl ** check whether this machine has BFD and liberty installed (used for debugging)
+dnl    the order of these tests matters: bfd needs liberty
+AC_CHECK_LIB(iberty, xmalloc)
+AC_CHECK_LIB(bfd,    bfd_init)
+
 dnl ################################################################
 dnl Check for libraries
 dnl ################################################################