vcvrack: use the right compiler

[ryandesign (Ryan Carsten Schmidt)]

Looks like vcvrack isn't UsingTheRightCompiler. For example:

​https://build.macports.org/builders/ports-10.8_x86_64-builder/builds/23725/steps/install-port/logs/stdio

DEBUG: Using compiler 'MacPorts Clang 9.0'

But then:

cd glew-2.1.0/build && cmake -DCMAKE_INSTALL_PREFIX="/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_audio_vcvrack/vcvrack/work/Rack-1.1.6/dep" -DCMAKE_INSTALL_LIBDIR=lib ./cmake
-- The C compiler identification is AppleClang 5.1.0.5030040
-- The CXX compiler identification is AppleClang 5.1.0.5030040

[herbygillot (Herby Gillot)]

vcvrack is pulling down a bunch of 3rd-party Makefiles and directly running them with make -C <dir>. Likely environment / make variables aren't flowing between these Makefiles.

[ryandesign (Ryan Carsten Schmidt)]

In 8bfc6106ab999164a79b34f5a28d35db23391453/macports-ports (master):

vcvrack: Fix compiler selection

Decide which compiler we're going to use before we access the variables
for the compiler executables.

See: #60996

[ryandesign (Ryan Carsten Schmidt)]

That appears to have fixed the compiler selection, though the build still fails on many OS versions for other reasons.