archer build failure with llvm 9

[lee218llnl]

It looks like Archer fails to build with LLVM 9:

[ 26%] Building CXX object lib/CMakeFiles/LLVMArcher.dir/Transforms/Instrumentation/InstrumentParallel.cpp.o
/usr/workspace/lee218/delete/spack-ulna-openmpi/ArcherBuild/archer/lib/Transforms/Instrumentation/InstrumentParallel.cpp:188:45: error: no matching function for call to 'cast'
    Function* __tsan_default_suppressions = cast<Function>(M->getOrInsertFunction("__tsan_default_suppressions",
                                            ^~~~~~~~~~~~~~
/usr/workspace/lee218/delete/spack-ulna-openmpi/opt/spack/linux-rhel7-broadwell/gcc-8.1.0/llvm-9.0.0-7onw4vzicjqun2vojttomwc7egcfmsu4/include/llvm/Support/Casting.h:256:44: note: candidate function [with X = llvm::Function, Y = llvm::FunctionCallee] not viable: expects an l-value for 1st argument
inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
                                           ^
/usr/workspace/lee218/delete/spack-ulna-openmpi/opt/spack/linux-rhel7-broadwell/gcc-8.1.0/llvm-9.0.0-7onw4vzicjqun2vojttomwc7egcfmsu4/include/llvm/Support/Casting.h:249:1: note: candidate template ignored: requirement '!is_simple_type<llvm::FunctionCallee>::value' was not satisfied [with X = llvm::Function, Y = llvm::FunctionCallee]
cast(const Y &Val) {
^
/usr/workspace/lee218/delete/spack-ulna-openmpi/opt/spack/linux-rhel7-broadwell/gcc-8.1.0/llvm-9.0.0-7onw4vzicjqun2vojttomwc7egcfmsu4/include/llvm/Support/Casting.h:263:46: note: candidate template ignored: could not match 'Y *' against 'llvm::FunctionCallee'
inline typename cast_retty<X, Y *>::ret_type cast(Y *Val) {
                                             ^
/usr/workspace/lee218/delete/spack-ulna-openmpi/opt/spack/linux-rhel7-broadwell/gcc-8.1.0/llvm-9.0.0-7onw4vzicjqun2vojttomwc7egcfmsu4/include/llvm/Support/Casting.h:271:1: note: candidate template ignored: could not match 'unique_ptr<type-parameter-0-1, default_delete<type-parameter-0-1> >' against 'llvm::FunctionCallee'
cast(std::unique_ptr<Y> &&Val) {
^
/usr/workspace/lee218/delete/spack-ulna-openmpi/ArcherBuild/archer/lib/Transforms/Instrumentation/InstrumentParallel.cpp:204:15: error: no viable conversion from 'llvm::FunctionCallee' to 'llvm::Constant *'
    Constant* constant = M->getOrInsertFunction("__archer_get_omp_status",
              ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.
make[2]: *** [lib/CMakeFiles/LLVMArcher.dir/Transforms/Instrumentation/InstrumentParallel.cpp.o] Error 1
make[1]: *** [lib/CMakeFiles/LLVMArcher.dir/all] Error 2
make: *** [all] Error 2

This appears to be related to https://bugs.freedesktop.org/show_bug.cgi?id=109540. A proper fix may look something like the commit pointed to in the previous link: llvm-mirror/llvm@9ec60d7#diff-295d2c56655729b2bd6dc1dfca7c2f0e.