remove Cmake option for LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING

[bob.wilson]

Summary

This is a follow-up to my change in r295090, which added support for disabling these checks selectively based on setting the preprocessor macro without relying on the Cmake setting. Swift has moved over to use that approach, so we can clean up here and remove the Cmake setting.

[mehdi_amini]

I'm fine with this, I hope no one else started using it though...

[bob.wilson]

All the more reason to clean this up now!
r297109

CMakeLists.txt

 set(LLVM_ABI_BREAKING_CHECKS "WITH_ASSERTS" CACHE STRING
   "Enable abi-breaking checks.  Can be WITH_ASSERTS, FORCE_ON or FORCE_OFF.")
 
-option(LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING
-  "Disable abi-breaking checks mismatch detection at link-tim." OFF)
-
 option(LLVM_FORCE_USE_OLD_HOST_TOOLCHAIN
        "Set to ON to force using an old, unsupported host toolchain." OFF)
 

llvm/Config/abi-breaking.h.cmake

 /* Define to enable checks that alter the LLVM C++ ABI */
 #cmakedefine01 LLVM_ENABLE_ABI_BREAKING_CHECKS
 
-/* Define to disable the link-time checking of mismatch for
-   LLVM_ENABLE_ABI_BREAKING_CHECKS */
-#ifndef LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING
-#cmakedefine01 LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING
-#endif
+/* Allow selectively disabling link-time mismatch checking so that header-only
+   ADT content from LLVM can be used without linking libSupport. */
 #if !LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING
 
 // ABI_BREAKING_CHECKS protection: provides link-time failure when clients build