Add env variable giving an extra library location. #5

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 7s
🐧 Linux / Editor w/ Mono (target=editor)	41m 53s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	46m 16s
🍏 iOS / Template (target=template_release)	9m 21s
🤖 Android / Editor (target=editor)	25m 2s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	38m 4s
🍎 macOS / Editor (target=editor, tests=yes)	49s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	16m 14s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	31m 30s
🍎 macOS / Template (target=template_release)	39s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	17m 9s
🐧 Linux / Template w/ Mono (target=template_release)	6m 41s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	26m 7s
🐧 Linux / Minimal template (target=template_release, everything disabled)	15m 58s
🌐 Web / Template w/o threads (target=template_release, threads=no)	26m 24s
🏁 Windows / Editor (target=editor, tests=yes)	1m 56s
🏁 Windows / Template (target=template_release)	35m 16s
🪲 Godot CPP	0s
	5h 40m 26s

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