opencascade: Fix build against glibc 2.26

The header file xlocale.h has been removed in glibc 2.26.

Quoting the release notes[1]:

  * The nonstandard header <xlocale.h> has been removed. Most programs
    should use <locale.h> instead. If you have a specific need for the
    definition of locale_t with no other declarations, please contact
    libc-alpha@sourceware.org and explain.

Tested by building on x86_64-linux and it now succeeds.

[1]: https://sourceware.org/ml/libc-alpha/2017-08/msg00010.html

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @viric

pkgs/development/libraries/opencascade/default.nix

@@ -10,6 +10,12 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ mesa tcl tk file libXmu libtool qt4 ftgl freetype cmake ];
 
+  # Fix for glibc 2.26
+  postPatch = ''
+    sed -i -e 's/^\( *#include <\)x\(locale.h>\)//' \
+      src/Standard/Standard_CLocaleSentry.hxx
+  '';
+
   preConfigure = ''
     cmakeFlags="$cmakeFlags -DOCE_INSTALL_PREFIX=$out"
   '';