Fix bthread_usleep return unexpected error #896

Job	Run time
gcc-compile-with-boringssl	19m 58s
gcc-compile-with-cmake	2m 53s
gcc-compile-with-make	2m 37s
clang-compile-with-make	2m 55s
gcc-compile-with-bazel	16m 51s
gcc-compile-with-bazel-all-options	18m 58s
gcc-compile-with-cmake-all-options	5m 11s
gcc-compile-with-make-all-options	4m 29s
clang-compile-with-bazel	14m 8s
clang-compile-with-bazel-all-options	16m 59s
clang-compile-with-boringssl	20m 10s
clang-compile-with-cmake	2m 32s
clang-compile-with-cmake-all-options	4m 40s
clang-compile-with-make-all-options	4m 32s
clang-unittest	13m 35s
	2h 30m 28s

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