[lldb] add check for libcxx runtime

When enabling LLDB tests with `LLVM_ENABLE_RUNTIMES=libcxx` CMake will
fail with:

```
LLDB test suite requires libc++, but it is currently disabled.
```

The issue is that the targets in LLVM_ENABLE_RUNTIMES are configured
after the targets in LLVM_ENABLE_PROJECTS, so at this point the check
for the `cxx` target will fail. CMake will add a dependency for a target
that does not exist yet however, so by first checking for `libcxx` in
LLVM_ENABLE_RUNTIMES we ensure that the `cxx` target will be present at
build time.

Tested with:
```
% cmake -G Ninja \
    -C ~/local/llvm-project/lldb/cmake/caches/Apple-lldb-macOS.cmake \
    -DLLVM_ENABLE_PROJECTS="clang;lldb" -DLLVM_ENABLE_RUNTIMES="libcxx" \
    -DLIBCXX_INCLUDE_TESTS=NO ~/local/llvm-project/llvm
% ninja check-lldb
```

Reviewed By: smeenai, JDevlieghere

Differential Revision: https://reviews.llvm.org/D97227

diff --git a/lldb/test/CMakeLists.txt b/lldb/test/CMakeLists.txt
index 79fa05f..34fc377 100644 (file)
--- a/lldb/test/CMakeLists.txt
+++ b/lldb/test/CMakeLists.txt
@@ -106,7 +106,7 @@ if(TARGET clang)
     else()
       # We require libcxx for the test suite, so if we aren't building it,
       # try to provide a helpful error about how to resolve the situation.
-      if(NOT TARGET cxx)
+      if(NOT TARGET cxx AND NOT libcxx IN_LIST LLVM_ENABLE_RUNTIMES)
         if(LLVM_ENABLE_PROJECTS STREQUAL "")
           # If `LLVM_ENABLE_PROJECTS` is not being used (implying that we are
           # using the old layout), suggest checking it out.
@@ -118,8 +118,9 @@ if(TARGET clang)
           # If `LLVM_ENABLE_PROJECTS` is being used, suggest adding it.
           message(FATAL_ERROR
             "LLDB test suite requires libc++, but it is currently disabled. "
-            "Please add `libcxx` to `LLVM_ENABLE_PROJECTS` or disable tests "
-            "via `LLDB_INCLUDE_TESTS=OFF`.")
+            "Please add `libcxx` to `LLVM_ENABLE_PROJECTS` or "
+            "`LLVM_ENABLE_RUNTIMES`, or disable tests via "
+            "`LLDB_INCLUDE_TESTS=OFF`.")
         endif()
       endif()
       add_lldb_test_dependency(cxx)