Determining if the function pcap_get_pfring_id exists failed with the following output:
Change Dir: /var/tmp/portage/games-emulation/pcsx2-1.6.0/work/pcsx2-1.6.0_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/ninja cmTC_aa1b9 && [1/2] Building C object CMakeFiles/cmTC_aa1b9.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_aa1b9
FAILED: cmTC_aa1b9 
: && /usr/lib/llvm/10/bin/x86_64-pc-linux-gnu-clang  -m32 -O2 -pipe -march=native -frecord-gcc-switches -fno-diagnostics-color  -pipe -fvisibility=hidden -pthread -fno-builtin-strcmp -fno-builtin-memcmp -mfpmath=sse -Wall -Wextra -Wno-attributes -Wno-unused-function -Wno-unused-parameter -Wno-missing-field-initializers -Wno-overloaded-virtual -Wno-unused-value   -Wno-deprecated-register -Wno-c++14-extensions -Wstrict-aliasing -Wstrict-overflow=1  -D_FORTIFY_SOURCE=2  -Wformat -Wformat-security -DNDEBUG -DCHECK_FUNCTION_EXISTS=pcap_get_pfring_id -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0 -fuse-ld=lld   -rdynamic CMakeFiles/cmTC_aa1b9.dir/CheckFunctionExists.c.o -o cmTC_aa1b9  /usr/lib/libpcap.so && :
ld.lld: error: undefined symbol: pcap_get_pfring_id
>>> referenced by CheckFunctionExists.c
>>>               CMakeFiles/cmTC_aa1b9.dir/CheckFunctionExists.c.o:(main)
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.