build: preserves symbols during LTO with macOS linker
man ld -export_dynamic:
Preserves all global symbols in main executables during LTO.
Without this option, Link Time Optimization is allowed to inline
and remove global functions.
This option is used when a main executable may load a plug-in which
requires certain symbols from the main executable.
This fix should be backported to release lines that have ab71af34.
Bug: vercel/pkg#1155 Signed-off-by: Jesse Chan jc@linux.com