bthread set concurrency by tag #1184

Job	Run time
clang-compile-with-bazel-all-options	16m 57s
clang-compile-with-bazel	14m 48s
clang-compile-with-boringssl	19m 40s
clang-compile-with-cmake	2m 38s
clang-compile-with-make	2m 43s
clang-compile-with-cmake-all-options	4m 44s
clang-compile-with-make-all-options	4m 17s
clang-unittest	15m 1s
gcc-compile-with-bazel	15m 54s
gcc-compile-with-bazel-all-options	19m 33s
gcc-compile-with-boringssl	20m 13s
gcc-compile-with-cmake	2m 57s
gcc-compile-with-cmake-all-options	4m 52s
gcc-compile-with-make	2m 32s
gcc-compile-with-make-all-options	4m 15s
	2h 31m 4s

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