Merge pull request #11093 from ctiller/c++compat4

src/core/lib/support/cmdline.c

src/core/lib/support/histogram.c

src/core/lib/support/host_port.c

src/core/lib/support/string.c

src/core/lib/support/string_posix.c

src/core/lib/support/subprocess_posix.c

src/core/lib/support/thd_posix.c