Emscripten: re-enable the -pthread compiler flag #12949

Job	Run time
Code style check / Code style check	6s
CodeChecker / CodeChecker	31m 26s
IWYU / IWYU	3m 6s
MSVC / MSVC (SDL2 x86)	4m 32s
MSVC / MSVC (SDL2 x64)	4m 21s
SonarCloud Analyzer / SonarCloud Analyzer	0s
Android / Android	10m 35s
CMake / CMake (Linux SDL2)	2m 6s
CMake / CMake (macOS SDL2)	1m 36s
CMake / CMake (Windows SDL2)	4m 30s
Make / Make (Linux x86-64 SDL2 Release)	3m 0s
CMake / CMake (macOS SDL2 App Bundle)	1m 52s
Make / Make (PS Vita)	10m 1s
Make / Make (Linux x86-64 SDL2 Debug)	3m 4s
Make / Make (Linux ARM64 SDL2 Release)	4m 21s
Make / Make (Nintendo Switch)	3m 16s
Make / Make (Linux ARM64 SDL2 Debug)	4m 30s
Make / Make (Emscripten)	3m 57s
Make / Make (macOS SDL2)	3m 53s
Make / Make (macOS SDL2 App Bundle)	1m 39s
	1h 41m 51s

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