Add missing `#include <dlfcn.h>` (required by dlsym) #353

Job	Run time
Linux (GLideN64 (x64 Mupen64Plus-CLI))	3m 10s
Windows (GLideN64 (x64 Project64-Qt))	7m 15s
Linux (GLideN64 (x64 Mupen64Plus-Qt))	3m 7s
Windows (GLideN64 (x86 Project64-Qt))	6m 32s
Windows (GLideN64 (x64 Project64-WTL))	5m 3s
Windows (GLideN64 (x86 Project64-WTL))	4m 52s
Windows (GLideN64 (x64 Mupen64Plus-CLI))	4m 33s
Windows (GLideN64 (x86 Mupen64Plus-CLI))	4m 7s
Windows (GLideN64 (x64 Mupen64Plus-Qt))	7m 15s
Release	0s
	45m 54s

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