Add some #undef's to math.in.h, for AIX with xlc.

[Ralf Wildenhues]

AIX 5.3 needs a number of #undef's in math.in.h, in order to compile,
but I'm not sure whether that is the right fix, or some other logic is
wrong.

What do you need to know to analyze this?

Thanks,
Ralf

    Add some #undef's to math.in.h, for AIX with xlc.
    
    * lib/math.in.h (acosl, asinl, atanl, expl, sqrtl, tanl):
    Undefine before declaring them, for AIX 5.3 with xlc.

diff --git a/lib/math.in.h b/lib/math.in.h
index 7f09424..f9e62b8 100644
--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -119,6 +119,7 @@ extern double frexp (double x, int *expptr) _GL_ARG_NONNULL 
((2));
 
 
 #if @GNULIB_MATHL@ || !...@have_decl_acosl@
+#undef acosl
 extern long double acosl (long double x);
 #endif
 #if !...@gnulib_mathl@ && defined GNULIB_POSIXCHECK
@@ -131,6 +132,7 @@ extern long double acosl (long double x);
 
 
 #if @GNULIB_MATHL@ || !...@have_decl_asinl@
+#undef asinl
 extern long double asinl (long double x);
 #endif
 #if !...@gnulib_mathl@ && defined GNULIB_POSIXCHECK
@@ -143,6 +145,7 @@ extern long double asinl (long double x);
 
 
 #if @GNULIB_MATHL@ || !...@have_decl_atanl@
+#undef atanl
 extern long double atanl (long double x);
 #endif
 #if !...@gnulib_mathl@ && defined GNULIB_POSIXCHECK
@@ -195,6 +198,7 @@ extern long double cosl (long double x);
 
 
 #if @GNULIB_MATHL@ || !...@have_decl_expl@
+#undef expl
 extern long double expl (long double x);
 #endif
 #if !...@gnulib_mathl@ && defined GNULIB_POSIXCHECK
@@ -341,6 +345,7 @@ extern long double sinl (long double x);
 
 
 #if @GNULIB_MATHL@ || !...@have_decl_sqrtl@
+#undef sqrtl
 extern long double sqrtl (long double x);
 #endif
 #if !...@gnulib_mathl@ && defined GNULIB_POSIXCHECK
@@ -353,6 +358,7 @@ extern long double sqrtl (long double x);
 
 
 #if @GNULIB_MATHL@ || !...@have_decl_tanl@
+#undef tanl
 extern long double tanl (long double x);
 #endif
 #if !...@gnulib_mathl@ && defined GNULIB_POSIXCHECK