MSVC sanitizers about cnl

[johnmcfarlane]

MSVC sanitizers are not ready.

ASanitizer is of little use in a statically-sized numbers library anyway. Also, it doesn't appear to run reliably.
UBSan doesn't exist yet.
A few checks are available using the /RTC flags but they are not unit-test friendly. They could be enabled with

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index dd8550ae..f3774f6d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -298,8 +298,11 @@ jobs:
       - name: Install dependencies
         working-directory: ${{runner.workspace}}/build
         run: |
+          $sanitize = ("${{matrix.build_type}}" -eq "Debug")
+          echo $sanitize
           conan install `
             --build=missing `
+            --options sanitize=$sanitize `
             --profile:build $env:GITHUB_WORKSPACE/.github/conan/profiles/${{matrix.build-profile}} `
             --profile:host $env:GITHUB_WORKSPACE/.github/conan/profiles/${{matrix.host-profile}} `
             --settings:build build_type=Release `
diff --git a/test/toolchain/msvc.cmake b/test/toolchain/msvc.cmake
index 2dd2bc66..73b398aa 100644
--- a/test/toolchain/msvc.cmake
+++ b/test/toolchain/msvc.cmake
@@ -6,4 +6,6 @@ set(EXCEPTION_DISABLED_FLAGS "/GR- -DBOOST_NO_EXCEPTIONS -DBOOST_NO_RTTI")
 set(INT128_ENABLED_FLAGS "")
 set(INT128_DISABLED_FLAGS "")
 
+set(SANITIZE_ENABLED_CXX_FLAGS "/RTCcsu -D_ALLOW_RTCc_IN_STL")
+
 set(SAMPLE_CXX_FLAGS "/wd4018")

but this triggers dialogues inside tests designed to illustrate UB or test that sanitizers trap.

[johnmcfarlane]

AddressSanitizer changes (as far as I got):

diff --git a/test/toolchain/msvc.cmake b/test/toolchain/msvc.cmake
index 2dd2bc66..12050502 100644
--- a/test/toolchain/msvc.cmake
+++ b/test/toolchain/msvc.cmake
@@ -6,4 +6,7 @@ set(EXCEPTION_DISABLED_FLAGS "/GR- -DBOOST_NO_EXCEPTIONS -DBOOST_NO_RTTI")
 set(INT128_ENABLED_FLAGS "")
 set(INT128_DISABLED_FLAGS "")
 
+set(SANITIZE_ENABLED_CXX_FLAGS "/fsanitize=address /fsanitize-address-use-after-return /INCREMENTAL:NO /Zi")
+set(SANITIZE_ENABLED_LINKER_FLAGS "/DEBUG")
+
 set(SAMPLE_CXX_FLAGS "/wd4018")