Still getting libplacebo not found using pkg-config error

[kwaaak]

    @kevmitch I've adapted the scripts to support the `--wipe` functionality from your PR.

-lstd++ I added to both ffmpeg and mpv as they may both link against libplacebo, which may have glslang enabled.

I'd get an error from pkg-config when configuring ffmpeg without -lstd++:

/usr/lib64/gcc/x86_64-suse-linux/12/../../../../x86_64-suse-linux/bin/ld: /home/zeromind/src/github.com/zeromind/mpv-build/build_libs/lib/libplacebo.a(glsl_glslang.cc.o): undefined reference to symbol '_ZTVN10__cxxabiv117__class_type_infoE@@CXXABI_1.3'
/usr/lib64/gcc/x86_64-suse-linux/12/../../../../x86_64-suse-linux/bin/ld: /usr/lib64/libstdc++.so.6: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
ERROR: libplacebo >= 4.192.0 not found using pkg-config

Originally posted by @zeromind in #188 (comment)

I was still getting this error, everything builds fine after doing a sudo apt remove glslang-dev
I assume libplacebo is built without it now and successfully picked up by ffmpeg's configure

Manually checking with pkg-config returned no error, maybe it is worth investigating more because the error is not what it seems.

[Traneptora]

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