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  TODO: .ci/Makefile is obsolete now, as well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/project/toolchain.py b/project/toolchain.py
new file mode 100644
index 0000000..d931c6b
--- /dev/null
+++ b/project/toolchain.py
@@ -0,0 +1,45 @@
+# Copyright (c) 2020 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is part of the "cmake-common" project.
+# For details, see https://github.com/egor-tensin/cmake-common.
+# Distributed under the MIT License.
+
+'''Supported platform/build system/compiler combinations include, but are not
+limited to:
+
+* Linux / make / Clang,
+* Linux / make / GCC,
+* Linux / make / MinGW-w64,
+* Windows / make / Clang (clang.exe & clang++.exe),
+* Windows / make / Clang (clang-cl.exe, Boost 1.69.0 or higher only),
+* Windows / make / MinGW-w64,
+* Windows / msbuild / MSVC,
+* Cygwin / make / Clang,
+* Cygwin / make / GCC,
+* Cygwin / make / MinGW-w64.
+'''
+
+import argparse
+from enum import Enum
+
+
+class ToolchainType(Enum):
+    AUTO = 'auto'   # This most commonly means GCC on Linux and MSVC on Windows.
+    MSVC = 'msvc'   # Force MSVC.
+    GCC = 'gcc'     # Force GCC.
+    MINGW = 'mingw' # As in MinGW-w64; GCC with the PLATFORM-w64-mingw32 prefix.
+    CLANG = 'clang'
+    CLANG_CL = 'clang-cl'
+
+    def __str__(self):
+        return self.value
+
+    @staticmethod
+    def all():
+        return tuple(ToolchainType)
+
+    @staticmethod
+    def parse(s):
+        try:
+            return ToolchainType(s)
+        except ValueError:
+            raise argparse.ArgumentTypeError(f'invalid toolset: {s}')