Go1.21 uses PGO by default, if the file default.pgo exists. > The -pgo build flag now defaults to -pgo=auto, and the restriction of specifying a single main pa

Go1.21 uses PGO by default, if the file default.pgo exists. > The -pgo build flag now defaults to -pgo=auto, and the restriction of specifying a single main package on the command line is now removed. If a file named default.pgo is present in the main package's directory, the go command will use it to enable profile-guided optimization for building the corresponding program.