AIX build is broken

[andrewkirillov-ibm]

I did this

Building curl 8.11.0 on AIX system using XL C compiler:
https://www.ibm.com/docs/en/xl-c-and-cpp-aix/16.1?topic=cc-highly-configurable-compiler

export PATH=$PATH:/opt/IBM/xlc/16.1.0/bin
export CC=xlc_r
./configure --without-ssl --without-libpsl
make

This results in a failed build:

"var.h", line 30.8: 1506-334 (S) Identifier var has already been defined on line 64 of "/usr/include/sys/var.h".
make: The error code from the last command is 1.

The reason for this failure is a recent fix to #14880. In that fix we now include pthread.h from curl_setup.h The problem is that AIX systems have a sys/var.h system header. That header gets included through a chain with pthread.h. Also that header defines a "struct var" type. CURL also defines "struct var" in src/var.h. And so, as we now pull pthreads.h from one of the main curl headers, the system var structures conflicts with the curl's one.

I expected the following

Clean build

curl/libcurl version

8.11.0

operating system

AIX 7.2
IBM XL C/C++ for AIX, V16.1.0

[andrewkirillov-ibm]

A quick dirty fix could be removing pthread.h from curl_setup.h, which proves to work. However:

1. There was a reason it was done that way.
2. It will only delay the problem. Once pthread.h and src/var.h get included together, we'll get back to the problem.

As struct var usage is limited mostly to var.c, I would suggest renaming the structure.