[libunwind] [libunwind][libc++][libc++abi] Add cross-compilation flags to tests (PR #67201)

[Alexander Richardson via cfe-commits]

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@@ -45,10 +45,10 @@ config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include} -I %{libcxx}/test/support'
+    '@CMAKE_CXX_FLAGS_INIT@ -nostdinc++ -I %{include} -I %{libcxx}/test/support'
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arichardson wrote:

My original approach was to add a target flag (https://github.com/llvm/llvm-project/pull/65517) but @ldionne wasn't keen on that approach.

https://github.com/llvm/llvm-project/pull/67201