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  TODO: .ci/Makefile is obsolete now, as well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, 44 insertions, 0 deletions

diff --git a/.github/actions/check-boost-bootstrapped/action.yml b/.github/actions/check-boost-bootstrapped/action.yml
new file mode 100644
index 0000000..73f44a9
--- /dev/null
+++ b/.github/actions/check-boost-bootstrapped/action.yml
@@ -0,0 +1,44 @@
+name: Check that Boost was bootstrapped
+description: Check that Boost was bootstrapped
+runs:
+  using: composite
+  steps:
+    - run: |
+        echo '----------------------------------------------------------------'
+        echo 'bootstrap.log'
+        echo '----------------------------------------------------------------'
+        $path = Join-Path $env:BOOST_DIR 'bootstrap.log'
+        cat $path
+      shell: pwsh
+    - run: |
+        echo ''
+        echo '----------------------------------------------------------------'
+        echo 'project-config.jam'
+        echo '----------------------------------------------------------------'
+        $path = Join-Path $env:BOOST_DIR 'project-config.jam'
+        if (Test-Path $path -Type Leaf) {
+            cat $path
+        }
+      shell: pwsh
+    - run: |
+        echo ''
+        echo '----------------------------------------------------------------'
+        echo 'Checking that b2 executable was built'
+        echo '----------------------------------------------------------------'
+        $name = 'b2'
+        $path = Join-Path $env:BOOST_DIR $name
+
+        $exists_plain = Test-Path $path -Type Leaf
+        $exists_exe = Test-Path "${path}.exe" -Type Leaf
+        $exists = if ($env:CI_HOST_CYGWIN) {
+            $exists_plain -or $exists_exe
+        } elseif ($env:CI_HOST_WINDOWS) {
+            $exists_exe
+        } else {
+            $exists_plain
+        }
+
+        if (-not $exists) {
+            throw "b2 executable wasn't found"
+        }
+      shell: pwsh