[lldb] Let LLDB depend on intrinsics_gen to fix non-deterministic module build failures

Summary:
When building with modules we currently fail randomly to build LLDB's modules and get error messages like below:
```
In file included from <module-includes>:1:
In file included from llvm-project/llvm/include/llvm/IR/Argument.h:18:
llvm-project/llvm/include/llvm/IR/Attributes.h:74:14: fatal error: 'llvm/IR/Attributes.inc' file not found
    #include "llvm/IR/Attributes.inc"
             ^~~~~~~~~~~~~~~~~~~~~~~~
...
In file included from llvm-project/lldb/source/Plugins/ABI/SysV-arm/ABISysV_arm.cpp:9:
llvm-project/lldb/source/Plugins/ABI/SysV-arm/ABISysV_arm.h:12:10: fatal error: could not build module 'lldb_Wrapper'
```

The reason for this is that our source files can include Clang headers which in turn include files like Attributes.inc which
are generated by intrinsics_gen. However, it seems Clang can't express this dependency in its CMake code, so intrinsics_gen
is actually not guaranteed to be built before we start parsing LLDB source files and Clang headers. Clang worked around this
by letting all libraries depend on intrinsics_gen, which at least lets their builds pass.

As I haven't figured out how to solve these dependencies properly and I want to get the LLDB+Modules build green,
I suggest we copy Clang's hack until we figure out how to get Clang's dependencies right.

Reviewers: sgraenitz, aprantl, JDevlieghere

Reviewed By: JDevlieghere

Subscribers: mgorny, javed.absar, kristof.beyls, mgrang, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D66208

llvm-svn: 368975

Author: Teemperor

lldb/CMakeLists.txt

@@ -40,6 +40,15 @@ if (NOT LLDB_DISABLE_PYTHON)
   add_subdirectory(scripts)
 endif ()
 
+# We need the headers generated by instrinsics_gen before we can compile
+# any source file in LLDB as the imported Clang modules might include
+# some of these generated headers. This approach is copied from Clang's main
+# CMakeLists.txt, so it should kept in sync the code in Clang which was added
+# in llvm-svn 308844.
+if(LLVM_ENABLE_MODULES AND NOT LLDB_BUILT_STANDALONE)
+  list(APPEND LLVM_COMMON_DEPENDS intrinsics_gen)
+endif()
+
 if(CMAKE_CROSSCOMPILING AND LLDB_BUILT_STANDALONE)
   set(LLVM_USE_HOST_TOOLS ON)
   include(CrossCompile)