amap: Fix amap_split #892

Job	Run time
build-minimal-sysroots (x86_64)	52s
build-minimal-sysroots (riscv64)	56s
build-minimal-sysroots (arm64)	51s
build-toolchains (ubuntu-latest, x86_64, gnu)	35s
build-toolchains (ubuntu-latest, riscv64, gnu)	37s
build-toolchains (ubuntu-latest, arm64, gnu)	43s
build-toolchains (ubuntu-20.04, x86_64, gnu)	31s
build-toolchains (ubuntu-20.04, riscv64, gnu)	36s
build-toolchains (ubuntu-20.04, arm64, gnu)	26s
build-toolchains (macos-latest, x86_64, gnu)	1m 26s
build-toolchains (macos-latest, riscv64, gnu)	1m 11s
build-toolchains (macos-latest, arm64, gnu)	47s
build-toolchains (ubuntu-latest, llvm, all)	1m 9s
build-llvm-riscv64	2m 28s
build-riscv	2m 20s
build-llvm	2m 37s
build-llvm-arm64	2m 24s
build	2m 46s
run-x86_64	0s
build-arm64	2m 56s
run-x86_64-llvm	0s
run-riscv	0s
run-riscv64-llvm	0s
	26m 11s

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