[CMake] Fix ExtensionDependencies.inc with multiple extensions

When polly is enabled and LLVM_BYE_LINK_INTO_TOOLS=ON is on, ExtensionDependencies.inc does not compile.

$ ninja tools/llvm-config/CMakeFiles/llvm-config.dir/llvm-config.cpp.o
tools/llvm-config/ExtensionDependencies.inc:8:1: error: excess elements in struct initializer
{{"Bye", {"Bye",nullptr}}},

ExtensionDependencies.inc pre-patch:
  std::array<ExtensionDescriptor, 2> AvailableExtensions{
  {{"Polly", {"support", "core", ...,nullptr}}},
  {{"Bye", {"Bye",nullptr}}},
  };

ExtensionDependencies.inc with this patch:
  std::array<ExtensionDescriptor, 2> AvailableExtensions{
  ExtensionDescriptor{"Polly", {"support", "core", ...,nullptr}},
  ExtensionDescriptor{"Bye", {"Bye",nullptr}},
  };

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D91641