Add missing `#include <dlfcn.h>` (required by dlsym) #358

Job	Run time
Linux (GLideN64 (x64 Mupen64Plus-CLI))	2m 26s
Windows (GLideN64 (x64 Project64-Qt))	7m 16s
Linux (GLideN64 (x64 Mupen64Plus-Qt))	4m 17s
Windows (GLideN64 (x86 Project64-Qt))	6m 32s
Windows (GLideN64 (x64 Project64-WTL))	4m 48s
Windows (GLideN64 (x86 Project64-WTL))	4m 56s
Windows (GLideN64 (x64 Mupen64Plus-CLI))	4m 37s
Windows (GLideN64 (x86 Mupen64Plus-CLI))	4m 38s
Windows (GLideN64 (x64 Mupen64Plus-Qt))	6m 59s
Release	18s
	46m 47s

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