Move LLVM_ENABLE_ABI_BREAKING_CHECKS to its own file

[echristo]

Summary

Move LLVM_ENABLE_ABI_BREAKING_CHECKS variables to their own file so that you don't have to link Error.o and all of its dependencies.

Tested by building everything.

[lattner]

Awesome, thanks Eric! This is very useful for projects that want to use LLVM Support library but also care about codesize.

[dblaikie]

Might be worth having some more detail in the commit message to explain why -ffunction-sections/-gc-sections isn't sufficient to remove the binary size increase.

(also, might be worth tracking down the global initializers that were causing this to have a binary size cost - seeing if those can be removed too)

[echristo]

In D67387#1665052, @dblaikie wrote:

Might be worth having some more detail in the commit message to explain why -ffunction-sections/-gc-sections isn't sufficient to remove the binary size increase.

(also, might be worth tracking down the global initializers that were causing this to have a binary size cost - seeing if those can be removed too)

Good idea btw, I did that before I committed :)

llvm/lib/Support/ABIBreak.cpp

+//===----- lib/Support/ABIBreak.cpp - EnableABIBreakingChecks -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Config/abi-breaking.h"
+
+#ifndef _MSC_VER
+namespace llvm {
+
+// One of these two variables will be referenced by a symbol defined in
+// llvm-config.h. We provide a link-time (or load time for DSO) failure when
+// there is a mismatch in the build configuration of the API client and LLVM.
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+int EnableABIBreakingChecks;
+#else
+int DisableABIBreakingChecks;
+#endif
+
+} // end namespace llvm
+#endif

llvm/lib/Support/CMakeLists.txt

 
 add_llvm_library(LLVMSupport
   AArch64TargetParser.cpp
+  ABIBreak.cpp
   ARMTargetParser.cpp
   AMDGPUMetadata.cpp
   APFloat.cpp

llvm/lib/Support/Error.cpp

 LLVMErrorTypeId LLVMGetStringErrorTypeId() {
   return reinterpret_cast<void *>(&StringError::ID);
 }
-
-#ifndef _MSC_VER
-namespace llvm {
-
-// One of these two variables will be referenced by a symbol defined in
-// llvm-config.h. We provide a link-time (or load time for DSO) failure when
-// there is a mismatch in the build configuration of the API client and LLVM.
-#if LLVM_ENABLE_ABI_BREAKING_CHECKS
-int EnableABIBreakingChecks;
-#else
-int DisableABIBreakingChecks;
-#endif
-
-} // end namespace llvm
-#endif

llvm/utils/gn/secondary/llvm/lib/Support/BUILD.gn

   ]
   sources = [
     "AArch64TargetParser.cpp",
+    "ABIBreak.cpp",
     "AMDGPUMetadata.cpp",
     "APFloat.cpp",
     "APInt.cpp",