build: explicitly disable building with zstd #87

Job	Run time
build-llvm (ubuntu-22.04, Release)	5m 24s
build-llvm (macos-15-intel, Release)	12m 27s
build-llvm (macos-14, Release)	6m 20s
build-llvm (ubuntu-latest, Release)	5m 35s
build-llvm (windows-latest, Release)	10m 34s
test-llvm-z80 (ubuntu-22.04, Release)	1m 34s
build-clang (ubuntu-latest, Release)	4m 1s
test-llvm-z80 (macos-14, Release)	2m 12s
build-clang (windows-latest, Release)	7m 29s
test-llvm-z80 (macos-15-intel, Release)	3m 25s
build-clang (macos-14, Release)	4m 32s
build-clang (macos-15-intel, Release)	7m 45s
test-llvm-z80 (ubuntu-latest, Release)	1m 27s
build-clang (ubuntu-22.04, Release)	4m 6s
nightly	28s
	1h 17m 19s

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