Add /bigobj for SPIRV dialect on MSVC.

[stellaraccident]

Summary

This object file has grown beyond the default limit, and elsewhere in LLVM, we seem to be setting this flag as a one-off, so continuing that here.

[mehdi_amini]

Do why know why is this object so large? This may be an indication of something underlying to look at anyway.

[stellaraccident]

In D77002#1948310, @mehdi_amini wrote:

Do why know why is this object so large? This may be an indication of something underlying to look at anyway.

Afaik, it is not so much "large" as it is quirks about PE object files in debug builds with large string tables. From what I've read, VC emits a lot of sections in that case, and it is the total number of sections that overflows without /bigobj. But to answer your question, no, I did no further analysis. Most projects I work on just uncategorically set /bigobj globally for Windows/VC builds. The only reason not to do so, I am told, is compatibility with tools from prior to about 2005.

mlir/lib/Dialect/SPIRV/CMakeLists.txt

+if (MSVC)
+  set_source_files_properties(SPIRVDialect.cpp PROPERTIES COMPILE_FLAGS /bigobj)
+endif()
+
 set(LLVM_TARGET_DEFINITIONS SPIRVCanonicalization.td)
 mlir_tablegen(SPIRVCanonicalization.inc -gen-rewriters)
 add_public_tablegen_target(MLIRSPIRVCanonicalizationIncGen)
 
 add_mlir_dialect_library(MLIRSPIRV
   LayoutUtils.cpp
   SPIRVAttributes.cpp
   SPIRVCanonicalization.cpp