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  TODO: .ci/Makefile is obsolete now, as well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, 45 insertions, 0 deletions

diff --git a/.github/actions/run-example-boost/action.yml b/.github/actions/run-example-boost/action.yml
new file mode 100644
index 0000000..0dd9f44
--- /dev/null
+++ b/.github/actions/run-example-boost/action.yml
@@ -0,0 +1,45 @@
+name: Run examples/boost
+description: Run examples/boost
+inputs:
+  path:
+    description: Installation directory
+    required: true
+runs:
+  using: composite
+  steps:
+    - run: |
+        New-Variable path -Value '${{ inputs.path }}' -Option Constant
+
+        if ($env:CI_HOST_LINUX -and -not $env:CI_TARGET_LINUX) {
+            echo 'Not going to do that on Linux/MinGW'
+            exit
+        }
+
+        $relative_test = 'test.txt'
+        $absolute_test = Join-Path (Get-Location).Path 'test.txt'
+
+        $exe_path = (Join-Path $path 'bin' 'foo')
+        if (-not $env:CI_TARGET_CYGWIN) {
+            $exe_path += $env:CI_EXE_EXT
+        }
+
+        $argv0 = $exe_path
+        if ($env:CI_TARGET_CYGWIN) {
+            # Apparently, Cygwin programs convert argv[0] when executing native
+            # programs or being executed by them.
+            $argv0 = cygpath.exe -ua $argv0
+        }
+
+        $actual = & $exe_path $relative_test
+
+        echo 'Actual output:'
+        echo $actual
+
+        $expected = $argv0,$absolute_test
+        echo 'Expected output:'
+        echo $expected
+
+        if (Compare-Object $actual $expected -CaseSensitive) {
+            throw 'Unexpected output'
+        }
+      shell: pwsh