[Bug 260005] devel/wasi-libcxx: not built to spec and not really useable

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=260005

            Bug ID: 260005
           Summary: devel/wasi-libcxx: not built to spec and not really
                    useable
           Product: Ports & Packages
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Keywords: patch
          Severity: Affects Only Me
          Priority: ---
         Component: Individual Port(s)
          Assignee: ports-bugs@FreeBSD.org
          Reporter: cmt@freebsd.org
                CC: greg@unrelenting.technology
                CC: greg@unrelenting.technology
             Flags: maintainer-feedback?(greg@unrelenting.technology)

Created attachment 229684
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=229684&action=edit
disable exceptions and fix more feature flags in wasi-libcxx

platform is FreeBSD 13.0-RELEASE-p5, amd64, poudriere.

Trying to use wasi-libcxx (e.g. when building firefox beta with web assembly
sandbox) does not work:

  wasm-ld: error:
/usr/local/share/wasi-sysroot/lib/wasm32-wasi/libc++.a(string.cpp.o): undefined
symbol: __cxa_allocate_exception
  wasm-ld: error:
/usr/local/share/wasi-sysroot/lib/wasm32-wasi/libc++.a(string.cpp.o): undefined
symbol: __cxa_throw

wasi-sdk doesn't support exception, so more diagnosis:
wasi-libcxx was built with exceptions, there is no "-fno-exceptions" in the
build log, even as the port's Makefile specifies
"-DLIBCXX_ENABLE_EXCEPTIONS:BOOL=OFF -DLIBCXXABI_ENABLE_EXCEPTIONS:BOOL=OFF".
Digging further, I find that wasi-libcxx's CMakeFiles report

  -- Performing Test LIBCXX_SUPPORTS_FNO_EXCEPTIONS_FLAG
  -- Performing Test LIBCXX_SUPPORTS_FNO_EXCEPTIONS_FLAG - Failed

among others like that (e.g. "LIBCXX_SUPPORTS_WALL_FLAG - Failed"). More
digging ensues.

=> First:
CMakeFiles/CMakeErrors.log for libcxxabi reports

  Compiling the CXX compiler identification source file
"CMakeCXXCompilerId.cpp" failed.
  Compiler: /usr/bin/c++

That's the wrong compiler - base clang (11.0 in 13) does not know about
"--target=wasm32-wasi".
The reason is that this cmake was run in post-configure under CONFIGURE_ENV,
which does not contain CC/CXX/etc., that's only in MAKE_ENV by default (see any
poudrier log, all the environments are listed right at the top).
Anyways, that results in many of the compilier feature Tests failing, as the
compiler does not know about the target.

=> Second:
Even when using the correct compiler, many feature Tests still fail:

  wasm-ld: error: cannot open crt1.o: No such file or directory
  wasm-ld: error: unable to find library -lc++
  wasm-ld: error: unable to find library -lc++abi
  wasm-ld: error: unable to find library -lc

Well duh, we're getting into chicken-and-egg territory here.
The very ugly workaround is to just pass the Test results as flags to cmake,
which will then do the right thing (for at least some cases).

Attached patch will:
- bump PORTREVISION
- put CC/CFLAGS/CXX/CXXFLAGS into CONFIGURE_ENV
- pass the Test results into cmake (I'm being generous with the flags here, and
I hope I got it all correct - but then "it works for me").

Another nitpick: poudriere complains about

  pkg-static: DEVELOPER_MODE: Error: arch "FreeBSD:13:*" -- package installs
architecture specific files

but I'm not touching that right now, between this and firefox beta (it builds!)
I've enough for today.

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