Fix shaderc compilation with clang (#5622)

Using a patch already integrated upstream.

ports/shaderc/0001-Add-a-virtual-destructor.patch

@@ -0,0 +1,23 @@
+From 563bc6e87a43c38b5495469307922c768edbd191 Mon Sep 17 00:00:00 2001
+From: neil <neil@codeplay.com>
+Date: Thu, 1 Feb 2018 06:49:44 +0000
+Subject: [PATCH] Add a virtual destructor, otherwise Clang 6.0complains about
+ delete being called on an abstract class.
+
+---
+ libshaderc/include/shaderc/shaderc.hpp | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/libshaderc/include/shaderc/shaderc.hpp b/libshaderc/include/shaderc/shaderc.hpp
+index 1c557431..335f0df9 100644
+--- a/libshaderc/include/shaderc/shaderc.hpp
++++ b/libshaderc/include/shaderc/shaderc.hpp
+@@ -180,6 +180,8 @@ class CompileOptions {
+ 
+     // Handles shaderc_include_result_release_fn callbacks.
+     virtual void ReleaseInclude(shaderc_include_result* data) = 0;
++
++    virtual ~IncluderInterface() = default;
+   };
+ 
+   // Sets the includer instance for libshaderc to call during compilation, as

ports/shaderc/portfile.cmake

@@ -8,6 +8,7 @@ vcpkg_from_github(
     HEAD_REF master
     PATCHES
         0001-Do-not-generate-build-version.inc.patch
+        0001-Add-a-virtual-destructor.patch
 )
 
 file(COPY ${CMAKE_CURRENT_LIST_DIR}/CMakeLists.txt DESTINATION ${SOURCE_PATH}/third_party/glslang)