LLVMExegesisX86Tests: link to LLVMCore, too.

LLVMExegesisX86Tests: link to LLVMCore, too.

Fixes build for me.
Refs. D52054

[215/217] Linking CXX executable unittests/tools/llvm-exegesis/X86/LLVMExegesisX86Tests
FAILED: unittests/tools/llvm-exegesis/X86/LLVMExegesisX86Tests
: && /usr/bin/g++  -pipe -O2 -g0 -UNDEBUG -fPIC -fvisibility-inlines-hidden -Werror=date-time -std=c++11 -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wno-comment -fdiagnostics-color -ffunction-sections -fdata-sections -pipe -O2 -g0 -UNDEBUG  -fuse-ld=lld -Wl,--color-diagnostics -Wl,-allow-shlib-undefined     -Wl,-O3 -Wl,--gc-sections unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/AssemblerTest.cpp.o unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/AnalysisTest.cpp.o unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/SnippetGeneratorTest.cpp.o unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/RegisterAliasingTest.cpp.o unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/TargetTest.cpp.o  -o unittests/tools/llvm-exegesis/X86/LLVMExegesisX86Tests  -Wl,-rpath,/build/llvm-build-GCC-release/lib lib/libLLVMMC.so.8svn lib/libLLVMMCParser.so.8svn lib/libLLVMObject.so.8svn lib/libLLVMSymbolize.so.8svn lib/libLLVMX86CodeGen.so.8svn lib/libLLVMX86AsmParser.so.8svn lib/libLLVMX86AsmPrinter.so.8svn lib/libLLVMX86Desc.so.8svn lib/libLLVMX86Disassembler.so.8svn lib/libLLVMX86Info.so.8svn lib/libLLVMX86Utils.so.8svn lib/libLLVMSupport.so.8svn -lpthread lib/libgtest_main.so.8svn lib/libgtest.so.8svn -lpthread lib/libLLVMExegesis.so.8svn lib/libLLVMExegesisX86.so.8svn && :
ld.lld: error: undefined symbol: llvm::LLVMContext::~LLVMContext()
>>> referenced by AssemblerTest.cpp
>>>               unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/AssemblerTest.cpp.o:(exegesis::(anonymous namespace)::X86MachineFunctionGeneratorTest_DISABLED_JitFunction_Test::TestBody())

ld.lld: error: undefined symbol: llvm::LLVMContext::~LLVMContext()
>>> referenced by AssemblerTest.cpp
>>>               unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/AssemblerTest.cpp.o:(exegesis::(anonymous namespace)::X86MachineFunctionGeneratorTest_DISABLED_JitFunctionXOR32rr_Default_Test::TestBody())

ld.lld: error: undefined symbol: llvm::LLVMContext::~LLVMContext()
>>> referenced by AssemblerTest.cpp
>>>               unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/AssemblerTest.cpp.o:(void exegesis::MachineFunctionGeneratorBaseTest::Check<int, int, int, int, int, int, int, int>(exegesis::ExegesisTarget const&, llvm::ArrayRef<unsigned int>, llvm::MCInst, int, int, int, int, int, int, int, int))

ld.lld: error: undefined symbol: llvm::LLVMContext::~LLVMContext()
>>> referenced by AssemblerTest.cpp
>>>               unittests/tools/llvm-exegesis/X86/CMakeFiles/LLVMExegesisX86Tests.dir/AssemblerTest.cpp.o:(exegesis::(anonymous namespace)::X86MachineFunctionGeneratorTest_DISABLED_JitFunctionMOV32ri_Test::TestBody())
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

llvm-svn: 342182