shaderc-2018.0 includes this commit:
https://github.com/google/shaderc/commit/7193d2e8fcd8fab52af3f45468e653eaf6610edc

This shaderc commit relies on the following commits in glslang:
https://github.com/KhronosGroup/glslang/commit/3c3669904c4e6816974293ae9301f24de22ea336
https://github.com/KhronosGroup/glslang/commit/1f60c72c674d6a77043d03843563b4be63e80267

These glslang commits didn't make it into glslang-7.9.2888 release.
Thus in order to make shaderc-2018.0 build against current glslang,
we need to restore the NV_EXTENSIONS guard removed in 7193d2e8fcd8
and disable NV_EXTENSIONS support in the ebuild.

diff --git a/libshaderc_util/src/resources.cc b/libshaderc_util/src/resources.cc
index 458a63f..3cd9a66 100644
--- a/libshaderc_util/src/resources.cc
+++ b/libshaderc_util/src/resources.cc
@@ -116,6 +116,7 @@ const TBuiltInResource kDefaultTBuiltInResource = {
     /*.maxCullDistances = */ 8,                 // ARB_cull_distance.
     /*.maxCombinedClipAndCullDistances = */ 8,  // ARB_cull_distance.
     /*.maxSamples = */ 4,
+#ifdef NV_EXTENSIONS
     /* .maxMeshOutputVerticesNV = */ 256,
     /* .maxMeshOutputPrimitivesNV = */ 512,
     /* .maxMeshWorkGroupSizeX_NV = */ 32,
@@ -125,6 +126,7 @@ const TBuiltInResource kDefaultTBuiltInResource = {
     /* .maxTaskWorkGroupSizeY_NV = */ 1,
     /* .maxTaskWorkGroupSizeZ_NV = */ 1,
     /* .maxMeshViewCountNV = */ 4,
+#endif

     // This is the glslang TLimits structure.
     // It defines whether or not the following features are enabled.