Add asan support to cmake/nix

[lrstewart]

Description of changes:

Subset of #4048 to allow builds that use cmake or nix to enable ASAN.

Call-outs:

This doesn't remove the existing CI builds that use make for ASAN. It just allows new builds to use cmake or nix for ASAN.

Testing:

I intentionally created a memory leak in s2n_ktls_io_test and used nix to run the test.

• $ clean; S2N_CMAKE_OPTIONS="-DASAN=ON" configure output includes "Running tests with environment: S2N_DONT_MLOCK=1;S2N_ADDRESS_SANITIZER=1"
• $ unit reports:

Constructing a list of tests
Done constructing a list of tests
Updating test list for fixtures
Added 0 tests to meet fixture requirements
Checking test dependency graph...
Checking test dependency graph end
test 109
    Start 109: s2n_ktls_io_test

109: Test command: /home/ubuntu/s2n-tls/build/bin/s2n_ktls_io_test
109: Working Directory: /home/ubuntu/s2n-tls/tests/unit
109: Environment variables: 
109:  S2N_DONT_MLOCK=1
109:  S2N_ADDRESS_SANITIZER=1
109: Test timeout computed to be: 1500
109: 
109: =================================================================
109: ==1031096==ERROR: LeakSanitizer: detected memory leaks
109: 
109: Direct leak of 10 byte(s) in 1 object(s) allocated from:
109:     #0 0x7ffff768d7cf in __interceptor_malloc (/nix/store/5lp5v0sa76mhvc42bdc4z8vxwysp18r9-gcc-11.3.0-lib/lib/libasan.so.6+0xb17cf)
109:     #1 0x43a48c in s2n_mem_malloc_no_mlock_impl /home/ubuntu/s2n-tls/utils/s2n_mem.c:127
109:     #2 0x43af27 in s2n_realloc /home/ubuntu/s2n-tls/utils/s2n_mem.c:195
109:     #3 0x43b5b6 in s2n_alloc /home/ubuntu/s2n-tls/utils/s2n_mem.c:158
109:     #4 0x404566 in main /home/ubuntu/s2n-tls/tests/unit/s2n_ktls_io_test.c:156
109:     #5 0x7ffff6c0024d in __libc_start_call_main (/nix/store/9xfad3b5z4y00mzmk2wnn4900q0qmxns-glibc-2.35-224/lib/libc.so.6+0x2924d)
109: 
109: SUMMARY: AddressSanitizer: 10 byte(s) leaked in 1 allocation(s).
1/1 Test #109: s2n_ktls_io_test .................***Failed    1.69 sec

0% tests passed, 1 tests failed out of 1

Label Time Summary:
unit    =   1.69 sec*proc (1 test)

Total Test time (real) =   1.70 sec

The following tests FAILED:
	109 - s2n_ktls_io_test (Failed)
Errors while running CTest

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dougch]

Neat; this will be useful elsewhere.