[libFuzzer] extend -print_coverage to also print uncovered lines, functions, and files.

Example of output:
COVERAGE:
COVERED: in DSO2(int) /pathto/DSO2.cpp:6
COVERED: in DSO2(int) /pathto/DSO2.cpp:8
COVERED: in DSO1(int) /pathto/DSO1.cpp:6
COVERED: in DSO1(int) /pathto/DSO1.cpp:8
COVERED: in LLVMFuzzerTestOneInput /pathto/DSOTestMain.cpp:16
COVERED: in LLVMFuzzerTestOneInput /pathto/DSOTestMain.cpp:19
COVERED: in LLVMFuzzerTestOneInput /pathto/DSOTestMain.cpp:25
COVERED: in LLVMFuzzerTestOneInput /pathto/DSOTestMain.cpp:26
MODULE_WITH_COVERAGE: /pathto/libLLVMFuzzer-DSO1.so
UNCOVERED_LINE: in DSO1(int) /pathto/DSO1.cpp:9
UNCOVERED_FUNC: in Uncovered1()
MODULE_WITH_COVERAGE: /pathto/libLLVMFuzzer-DSO2.so
UNCOVERED_LINE: in DSO2(int) /pathto/DSO2.cpp:9
UNCOVERED_FUNC: in Uncovered2()
MODULE_WITH_COVERAGE: /pathto/LLVMFuzzer-DSOTest
UNCOVERED_LINE: in LLVMFuzzerTestOneInput /pathto/DSOTestMain.cpp:21
UNCOVERED_LINE: in LLVMFuzzerTestOneInput /pathto/DSOTestMain.cpp:27
UNCOVERED_FILE: /pathto/DSOTestExtra.cpp

Several things are not perfect here:
* we are using objdump+awk instead of sancov because sancov does not support DSOs yet.
* this breaks in the presence of ASAN_OPTIONS=strip_path_prefix=...
  (need to implement another API to get the module name by PC)

llvm-svn: 284554