GIANT CLUSTERFUCK OF A COMMIT

OK, this is epic.  I was basically just trying to a) support Clang and
b) add more test coverage.  _THREE MONTHS_ and a few hundred CI runs
later, this is what I came up with.  I don't know how it ended up being
what it is, but here we go.

Some highlights of the changes:

1) CI builds has been moved to GitHub Actions,
2) the entire notion of a toolchain has been reworked; it now supports
Clang on all platforms.

* .github: this directory contains the GitHub Actions workflow
scripts/actions.  In the process, I created like 6 external GitHub
actions, but it's still pretty massive.  An upside is that it covers
much more platform/toolchain combinations _and_ check a lot of the
expected post-conditions.  TODO: .ci/Makefile is obsolete now, as well
as .travis.yml and .appveyor.yml.

* common.cmake: added Clang support.  In the process, a great deal has
been learned about how CMake works; in particular, static runtime
support has been reworked to be more robust.

* project: the entire notion of a "toolchain" has been reworked.
Instead of a measly --mingw parameter, there's now a separate --toolset
parameter, which allows you to choose between GCC, Clang, MSVC, etc.
Both Boost and CMake build scripts were enhanced greatly to support
Clang and other toolchains in a more robust way.

1 files changed, 53 insertions, 0 deletions

diff --git a/.github/actions/build-boost/action.yml b/.github/actions/build-boost/action.yml
new file mode 100644
index 0000000..1f8a46c
--- /dev/null
+++ b/.github/actions/build-boost/action.yml
@@ -0,0 +1,53 @@
+name: Build Boost
+description: Build Boost
+inputs:
+  boost-dir:
+    description: Boost directory
+    required: false
+  toolset:
+    description: Toolset to use
+    required: false
+    default: auto
+  libraries:
+    description: Libraries to build
+    required: false
+  platform:
+    description: Target platform
+    required: false
+    default: x64
+  configuration:
+    description: Configuration to build
+    required: false
+    default: Debug
+runs:
+  using: composite
+  steps:
+    - run: |
+        $python = 'python'
+
+        $boost_dir = '${{ inputs.boost-dir }}'
+        if (-not $boost_dir) {
+            $boost_dir = $env:BOOST_DIR
+        }
+
+        $libraries = '${{ inputs.libraries }}'
+        $libraries = $libraries.Split(' ') | %{ "--with-$_" }
+        if (-not $libraries) {
+            Remove-Variable libraries
+        }
+
+        if ($env:CI_HOST_CYGWIN) {
+            $python = 'python3'
+            $boost_dir = cygpath.exe -ua $boost_dir
+        }
+
+        & $python `
+            -m project.boost.build `
+            --verbose `
+            --toolset '${{ inputs.toolset }}' `
+            --platform '${{ inputs.platform }}' `
+            --configuration '${{ inputs.configuration }}' `
+            -- `
+            $boost_dir `
+            $libraries
+      shell: pwsh