[libFuzzer] Make coverage.test work on ARM64

[yln]

Summary

This test instruments the following code with coverage, runs the fuzzer
once, and asserts that there are uncovered PCs. The ARM64 backend
optimizes this code using the csel (Conditional select) instruction,
which removes all branching from the resulting machine code. The test
then fails because we do not have any uncovered PCs. The easiest
solution for now is to turn off optimization for the DSOs used in this
test.

int DSO1(int a) {
  if (a < 123456)
    return 0;
  return 1;
}

rdar://47646400

[kcc]

LGTM

test/fuzzer/coverage.test

 # FIXME: Disabled on Windows because -fPIC cannot be used to compile for Windows.
 UNSUPPORTED: windows
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable  %S/NullDerefTest.cpp -o %t-NullDerefTest
-RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO1.cpp -fPIC %ld_flags_rpath_so1 -shared -o %dynamiclib1
-RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO2.cpp -fPIC %ld_flags_rpath_so2 -shared -o %dynamiclib2
+RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO1.cpp -fPIC %ld_flags_rpath_so1 -O0 -shared -o %dynamiclib1
+RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO2.cpp -fPIC %ld_flags_rpath_so2 -O0 -shared -o %dynamiclib2
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSOTestMain.cpp %S/DSOTestExtra.cpp %ld_flags_rpath_exe1 %ld_flags_rpath_exe2 -o %t-DSOTest
 
 CHECK: COVERAGE:
 CHECK: COVERED_FUNC: {{.*}}LLVMFuzzerTestOneInput {{.*}}NullDerefTest.cpp:14
 RUN: not %run %t-NullDerefTest -print_coverage=1 2>&1 | FileCheck %s
 
 RUN: %run %t-DSOTest -print_coverage=1 -runs=0 2>&1 | FileCheck %s --check-prefix=DSO
 DSO: COVERAGE:
-DSO-DAG: COVERED_FUNC:{{.*}}1{{.*}}
-DSO-DAG: COVERED_FUNC:{{.*}}2{{.*}}
+DSO-DAG: COVERED_FUNC:{{.*}}DSO1
+DSO-DAG: COVERED_FUNC:{{.*}}DSO2
 DSO-DAG: COVERED_FUNC:{{.*}}LLVMFuzzerTestOneInput{{.*}}DSOTestMain
-DSO-DAG: UNCOVERED_PC:{{.*}}1
-DSO-DAG: UNCOVERED_PC:{{.*}}2
+DSO-DAG: UNCOVERED_PC:{{.*}}DSO1
+DSO-DAG: UNCOVERED_PC:{{.*}}DSO2
 DSO-DAG: UNCOVERED_PC:{{.*}}DSOTestMain
 DSO-DAG: UNCOVERED_FUNC:{{.*}}Uncovered1