LLVM_ENABLE_ABI_BREAKING_CHECKS was disabled everywhere except for
Fuchsia. It triggered llvm::Error::assertIsChecked() in the new ORCv2
code because we're supposed to check Expected<> didn't return an error
by casting it to a bool, which we only do in Debug builds.

Since this option costs performance in Release builds and we don't want
to abort on errors (especially benign ones), it should only be enable
for Debug builds. This is also the default behavior for standalone
builds of LLVM:
https://llvm.org/docs/ProgrammersManual.html#abi-breaking-checks

Bug: b/171236524
Bug: chromium:1140854
Change-Id: If886fe9ef61d0f5392949d34a63ed3d7de7aa916
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/49908Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>