Help me understand dependents of libgcc-devel vs gcc13?

[Jim DeLaHunt]

Hi folks:

My "port upgrade outdated" commands were being blocked for a couple of 
weeks because a) port libgcc-devel was failing to build (see ticket 
#68421 [1]), and b) several ports were dependents of libgcc-devel for 
reasons I don't understand, and c) I had port libgcc-devel and not port 
gcc13 installed, for reasons I don't understand.

I blundered around until I fixed the problem (I think) by 1. 
deactivating libgcc-devel, blasting past the warning that five ports 
would break; then 2. installing port gcc13, which seemed to fill the 
hole left by libgcc-devel.

Could someone please help me understand:

Q: why are ports like fftw-3 reported as dependents of port 
libgcc-devel? I don't see anything in fftw-3's portfile[2] which 
mentions port libgcc-devel, or indeed any gcc or libgcc, are dependencies.

I suspect there is some behind-the-scenes dependency addition. Maybe it 
is behind the scenes because so many ports depend on C or C++ compilers. 
Where is this dependence addition documented? How should I as a user 
think of it?

Q: Why would I have libgcc-devel installed, and not have gcc13 (which 
has dependencies on ports libgcc and libgcc13) installed?

What sort of things cause the oblivious user to install libgcc-devel?

Q: was deactivating libgcc-devel and explicitly installing gcc13 the 
right way to fix this problem?

(I am using macOS 12.6 Monterey, so I think the portfiles tell me that 
gcc13 is the correct version.)

Note that the details of the breakage of port libgcc-devel don't matter 
to me if I don't need it, and can use something else instead.

Thanks in advance for helping me understand,
      —Jim DeLaHunt

[1] <https://trac.macports.org/ticket/68421>, ' libgcc-devel 
@14-20231001_0: build fails on arm64 "Configuration 
aarch64-apple-darwin21 not supported"'
[2] 
<https://github.com/macports/macports-ports/blob/4bafaba8c01a85cbc757cc75c8327ec2ea2a95f6/math/fftw-3/Portfile>

-- 
.    --Jim DeLaHunt, Vancouver, Canada