Improve type conversion error propagation/failure during LLVM lowering.
BEFORE
```
llvm-mlir/mlir/lib/Conversion/LLVMCommon/TypeConverter.cpp:304: SmallVector<mlir::Type, 5> mlir::LLVMTypeConverter::getMemRefDescriptorFields(mlir::MemRefType, bool): Assertion `isStrided(type) && "Non-strided layout maps must have been normalized away"' failed.
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
...
```
AFTER
```
<unknown>:0: error: integer overflow during size computation
<unknown>:0: error: Conversion to strided form failed either due to non-strided layout maps (which should have been normalized away) or other reasons
<unknown>:0: error: failed to legalize operation 'gpu.func' that was explicitly marked illegal
<unknown>:0: note: see current operation:
"gpu.func"() ( {
...
```
Reviewed By: ftynse
Differential Revision: https://reviews.llvm.org/D139072
5ceaeed659