[asan][test] Fix tests or mark XFAIL for MinGW target

After this change, `check-asan-dynamic` should pass on x86_64 MinGW
target, using the llvm-mingw toolchain.

The following is a list of issues fixed:

* `asan_str_test.cpp`: Exclude unintercepted functions on MinGW.
* `asan_test.cpp`: Work around regex limitation of gtest on Windows,
  which only affects MinGW target because `long double` has different
  size to `double`.
* `TestCases/Windows/report_after_syminitialize.cpp`: Added  build
  command specifically for MinGW.
* Other tests: Mark XFAIL for various reasons. Some of them need
  further investigation.

Differential Revision: https://reviews.llvm.org/D147059