Failed to build with -DUSE_STEAMWEBRTC=ON and cmake 3.20

# Steps to reproduce

1. Use cmake version 3.20.3 (I have manjaro linux installed)

2. Install dependecies `sudo pacman -S openssl protobuf`

3. Clone GameNetworkingSockets with `git clone --recursive https://github.com/ValveSoftware/GameNetworkingSockets`

4. Try to compile with p2p 

```

mkdir build && cd build

cmake -DUSE_STEAMWEBRTC=ON ..

```



# Error

```

-- Crypto library for AES/SHA256: OpenSSL

-- Crypto library for ed25519/curve25519: OpenSSL

-- Link-time optimization: OFF

-- Configuring done

CMake Error: install(EXPORT "GameNetworkingSockets" ...) includes target "GameNetworkingSockets" which requires target "steamwebrtc" that is not in any export set.

CMake Error: install(EXPORT "GameNetworkingSockets" ...) includes target "GameNetworkingSockets_s" which requires target "steamwebrtc" that is not in any export set.

-- Generating done

CMake Generate step failed.  Build files cannot be regenerated correctly.

```



# Full log

```

-- The C compiler identification is GNU 11.1.0

-- The CXX compiler identification is GNU 11.1.0

-- Detecting C compiler ABI info

-- Detecting C compiler ABI info - done

-- Check for working C compiler: /usr/lib/ccache/bin/cc - skipped

-- Detecting C compile features

-- Detecting C compile features - done

-- Detecting CXX compiler ABI info

-- Detecting CXX compiler ABI info - done

-- Check for working CXX compiler: /usr/lib/ccache/bin/c++ - skipped

-- Detecting CXX compile features

-- Detecting CXX compile features - done

-- Setting CMAKE_BUILD_TYPE to 'RelWithDebInfo' as none was specified.

-- Found OpenSSL: /usr/lib/libcrypto.so (found version "1.1.1k")  

-- OPENSSL_INCLUDE_DIR = /usr/include

-- Looking for EVP_MD_CTX_free

-- Looking for EVP_MD_CTX_free - found

-- Looking for EVP_PKEY_get_raw_public_key

-- Looking for EVP_PKEY_get_raw_public_key - found

-- Found Protobuf: /usr/lib/libprotobuf.so;-lpthread (found version "3.16.0") 

-- Found Threads: TRUE  

-- Looking for sys/types.h

-- Looking for sys/types.h - found

-- Looking for stdint.h

-- Looking for stdint.h - found

-- Looking for stddef.h

-- Looking for stddef.h - found

-- Check size of void*

-- Check size of void* - done

-- Performing Test _fvisibility_hidden_TEST

-- Performing Test _fvisibility_hidden_TEST - Success

-- Performing Test _fno_strict_aliasing_TEST

-- Performing Test _fno_strict_aliasing_TEST - Success

-- Performing Test _Wall_TEST

-- Performing Test _Wall_TEST - Success

-- Performing Test _Wno_unknown_pragmas_TEST

-- Performing Test _Wno_unknown_pragmas_TEST - Success

-- Performing Test _Wno_sign_compare_TEST

-- Performing Test _Wno_sign_compare_TEST - Success

-- Performing Test _Wno_unused_local_typedef_TEST

-- Performing Test _Wno_unused_local_typedef_TEST - Success

-- Performing Test _Wno_unused_const_variable_TEST

-- Performing Test _Wno_unused_const_variable_TEST - Success

-- Performing Test _Wno_nested_anon_types_TEST

-- Performing Test _Wno_nested_anon_types_TEST - Success

-- Performing Test _Wno_format_truncation_TEST

-- Performing Test _Wno_format_truncation_TEST - Success

-- Performing Test _Wstrict_prototypes_TEST

-- Performing Test _Wstrict_prototypes_TEST - Success

-- Performing Test _fvisibility_inlines_hidden_TEST

-- Performing Test _fvisibility_inlines_hidden_TEST - Success

-- Performing Test _Wno_reorder_TEST

-- Performing Test _Wno_reorder_TEST - Success

-- Performing Test _Wno_non_virtual_dtor_TEST

-- Performing Test _Wno_non_virtual_dtor_TEST - Success

-- Performing Test _Wno_zero_as_null_pointer_constant_TEST

-- Performing Test _Wno_zero_as_null_pointer_constant_TEST - Success

-- Performing Test _fno_exceptions_TEST

-- Performing Test _fno_exceptions_TEST - Success

-- Performing Test _fno_rtti_TEST

-- Performing Test _fno_rtti_TEST - Success

-- Crypto library for AES/SHA256: OpenSSL

-- Crypto library for ed25519/curve25519: OpenSSL

-- Link-time optimization: OFF

-- Configuring done

CMake Error: install(EXPORT "GameNetworkingSockets" ...) includes target "GameNetworkingSockets" which requires target "steamwebrtc" that is not in any export set.

CMake Error: install(EXPORT "GameNetworkingSockets" ...) includes target "GameNetworkingSockets_s" which requires target "steamwebrtc" that is not in any export set.

-- Generating done

CMake Generate step failed.  Build files cannot be regenerated correctly.

```

[]