cmake: build fails due to semicolons in CMAKE_C_FLAGS set by custom pcscd.cmake & openssl.cmake

[wfrisch]

yubico-piv-tool fails to build on a current openSUSE Tumbleweed (cmake version 3.28.1).

Symptom

Input:

git checkout yubico-piv-tool-2.5.1 
mkdir build/ && cd build/
cmake -DVERBOSE_CMAKE=1 ..
make VERBOSE=1

Output:

cd /home/wfrisch/src/yubico-piv-tool.git/build/lib && /usr/bin/cc -DOPENSSL_API_COMPAT=0x10000000L -DUSE_CERT_COMPRESS=\"1\" -I/home/wfrisch/src/yubico-piv-tool.git/lib -I/home/wfrisch/src/yubico-piv-tool.git/common -Wall -Werror -Wno-missing-braces -Wformat -Wformat-security -Wshadow -Wpointer-arith -Wmissing-prototypes -Wbad-function-cast -fstack-protector-all -Wno-pointer-sign -Wno-unused-result -DOPENSSL_LOAD_CONF;-I/usr/include -I/usr/include/PCSC -pthread -g -g2 -fno-omit-frame-pointer -std=gnu11 -fPIC -DSTATIC  -MD -MT lib/CMakeFiles/ykpiv.dir/ykpiv.c.o -MF CMakeFiles/ykpiv.dir/ykpiv.c.o.d -o CMakeFiles/ykpiv.dir/ykpiv.c.o -c /home/wfrisch/src/yubico-piv-tool.git/lib/ykpiv.c
cc: fatal error: no input files
compilation terminated.
/bin/sh: line 1: -I/usr/include: No such file or directory

This semicolon breaks the build: -DOPENSSL_LOAD_CONF;-I/usr/include.

Cause

As far as I can see, the root cause lies in the supplied custom modules pcscd.cmake and openssl.cmake. Both are using FindPkgConfig to retrieve the required CFLAGS and LDFLAGS. However FindPkgConfig returns lists, which are stored as semicolon-separated strings in CMake.

All but _FOUND may be a ;-list if the associated variable returned from pkg-config has multiple values.

Example:

include(FindPkgConfig)
pkg_check_modules(PCSC REQUIRED libpcsclite)
message("PCSC_LDFLAGS: ${PCSC_LDFLAGS}")

Output:

PCSC_LDFLAGS: -L/usr/lib64;-lpcsclite

I assume the developer of these custom modules was using a system where PCSC_CFLAGS and friends only contain one value and thus no semicolons.

Fix

The proper way to convert lists to strings in modern CMake is list(JOIN ...).

New in version 3.12.
Returns a string joining all list's elements using the glue string.

I will submit a PR shortly to address this bug in cmake/pcscd.cmake and cmake/openssl.cmake.

[aveenismail]

Thank you for bringing this issue to our attention and providing the PR to fix.

However, we still aim to have yubico-piv-tool build on older Linux platforms that do not support cmake version newer than 3.5 so this PR will be breaking building on those platforms. Now that we know about this issue though, we'll be looking into finding a way to fix it without having to use a newer cmake version.

Thank you again for the PR, it is highly appreciate it.