In -DBUILD_SHARED_LIBS=on builds, a component must specify its direct dependencies to satisfy -Wl,-z,defs (added by llvm/modules/HandleLLVMOptions.cmake).
Core is a direct dependency via transitive header inclusion:
ld.lld: error: undefined symbol: llvm::LLVMContext::LLVMContext()
>>> referenced by MachineSizeOptsTest.cpp
>>> unittests/Target/X86/CMakeFiles/X86Tests.dir/MachineSizeOptsTest.cpp.o:(testing::internal::TestFactoryImpl<(anonymous namespace)::MachineSizeOptsTest_Test_Test>::CreateTest())
MC is a direct dependency via transitive header inclusion:
ld.lld: error: undefined symbol: llvm::MCTargetOptions::MCTargetOptions()
>>> referenced by MachineSizeOptsTest.cpp
>>> unittests/Target/X86/CMakeFiles/X86Tests.dir/MachineSizeOptsTest.cpp.o:((anonymous namespace)::MachineSizeOptsTest::SetUp())
set(LLVM_LINK_COMPONENTS
Analysis
CodeGen
+ Core
+ MC
MIRParser
Support
Target