Disable -fsanitize=float-divide-by-zero in rtl_math_atanh

...which relies on division by zero producing inf, for atanh(1) = inf.  (As
tested by CppunitTest_sal_rtl.)

Change-Id: I0e5de8850ab4cbd05f83027c1eb548e2e0c9a9b2
Reviewed-on: https://gerrit.libreoffice.org/50613Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sal/rtl/math.cxx

@@ -1277,6 +1277,9 @@ double SAL_CALL rtl_math_log1p(double fValue) SAL_THROW_EXTERN_C()
 }
 
 double SAL_CALL rtl_math_atanh(double fValue) SAL_THROW_EXTERN_C()
+#if defined __clang__
+    __attribute__((no_sanitize("float-divide-by-zero"))) // atahn(1) -> inf
+#endif
 {
    return 0.5 * rtl_math_log1p(2.0 * fValue / (1.0-fValue));
 }