* upstream/pr/1171:
ci: install pkg-config in mingw-w64 CI
build: test ac_cv_header_sys_time_h once, reformat timer* macro checks
build: remove call to AC_C_CONST()
build: replace ntp_pkg_config macro with a call to PKG_PROG_PKG_CONFIG()
build: remove NTP_PKG_CONFIG call from libevent_mbedtls.m4
build: stop using the deprecated form of AC_OUTPUT()
build: quote args in AC_ARG_ENABLE & AS_HELP_STRING
build: remove call to AC_HEADER_TIME
build: call AC_PREREQ() first & quote argument
build: remove call to AC_PREFIX_DEFAULT
build: remove call to AC_PROG_GCC_TRADITIONAL