CXX-3180 add mingw-w64 GCC task coverage

[eramongodb]

Resolves CXX-3180 following DEVPROD-20813 and #1512. Verified by this patch.

This PR implements mingw-w64 GCC task coverage on Windows. This is in preparation for the followup resolution of CXX-2973 for pkg-config task coverage.

---

Most of the changes in this PR deal with consistently communicating the different CMake generators and toolchains to use when configuring and building example projects:

• example_projects_(cc|cxx): reuse CC (cc_compiler) and CXX (cxx_compiler) instead.
• example_projects_cxx_standard: reuse REQUIRED_CXX_STANDARD instead (default to minimum of 11 when unset).
• CMAKE_GENERATOR(_PLATFORM): reuse generator and platform instead (same as compile task).

Compile and link flags specific to example projects are still specified by example_projects_(cxxflags|ldflags).

The build.sh scripts are simplified to work regardless of CMake generator or toolchain. However, special-casing by single (non-Windows) vs. multi-config (Windows) generators is still necessary to avoid "unused by this project" warnings when specifying -DCMAKE_BUILD_TYPE=<config>.

Additional notes:

• libmongocrypt is pinned to a commit in the upcoming 1.17.1 / 1.18.0 release due to Use POSIX on Windows when building with mingw-w64 toolchain libmongocrypt#1098.
• Cannot build libmongocrypt using the usual build script helpers (i.e. compile-libmongocrypt.sh) due to hardcoded flags which assume MSVC on Windows.
• Linking the test_driver.exe executable alone can take up to 6 minutes (30% of task execution time)...! Unsure how to improve/avoid this behavior yet.
• Extended CMake max policy for test, example, and CMake compatibility projects to 4.99 to avoid requiring bumps with each new CMake minor release.
• Use -Wa,-mbig-obj as the mingw-w64 GCC equivalent to MSVC /bigobj (followup to Split collection_mocked.cpp test case into smaller functions #1509). Applied to all test executables.
• Removed unused vs_ver property for EVG distro definitions.

---

Finally, there is a consistent and ongoing EVG task failure for CSFLE tests with server 4.2 with mingw-w64 GCC due to errors of the following form (output is edited for readability):

src\mongocxx\test\spec\util.cpp:434: failed: explicitly with 4 messages:
  - 'Test path: data/client_side_encryption/legacy/awsTemporary.json'
  - 'Operation: {
      "name" : "insertOne",
      "arguments" : {
        "document" : { "_id" : 1, "encrypted_string" : "string0" } }
    }'
  - 'server_error := {
      "nInserted" : 0,
      "nMatched" : 0,
      "nModified" : 0,
      "nRemoved" : 0,
      "nUpserted" : 0,
      "writeErrors" : [ ]
    }'
  - 'unexpected exception: mongocryptd error: No suitable servers found: `serverSelectionTimeoutMS` expired: [connection refused calling hello on 'localhost:27020']. Topology type: Single: generic server error'

src\mongocxx\test\spec\util.cpp:431: failed:
  - test_util::tolowercase(error_msg).find(error_contains) < error_msg.length()
    - for: 18446744073709551615 (0xffffffffffffffff) < 182
  - with 4 messages:
    - 'Test path: data/client_side_encryption/legacy/awsTemporary.json'
    - 'Operation: { "name" : "insertOne", "arguments" : { "document" : { "_id" : 1, "encrypted_string" : "string0" } }, "result" : { "errorContains" : "security token" } }'
    - 'expected error message security token'
    - 'got: mongocryptd error: No suitable servers found: `serverSelectionTimeoutMS` expired: [connection refused calling hello on 'localhost:27020']. Topology type: Single: generic server error'

It is yet unclear to me why this error manifests only with mingw-w64 GCC on Windows. Perhaps there may be a cipher suite compatibility issue similar to CDRIVER-5998 or CDRIVER-4530?

[kevinAlbs]

Minor: but suggest using variable used for install path (which currently appears to have the same as ${mongoc_dir})

Suggested change

	echo "Installing libmongocrypt into ${mongoc_dir}..."
	echo "Installing libmongocrypt into ${mongoc_install_dir}..."

[kevinAlbs]

Finally, there is a consistent and ongoing EVG task failure for CSFLE tests with server 4.2 with mingw-w64 GCC

The "connection refused" makes me think this is a failure to connect over TCP. Idea: this may be from mongocryptd failing to spawn (maybe related to the form of MONGOCRYPTD_PATH?). But I am not sure why that would be specific to version 4.2.

Regardless: I think csfle on MinGW test coverage can be added in the future (I expect it may be more valuable testing in the C driver, since the platform specific CSFLE code is likely limited to the C driver + libmongocrypt).