[cmake] don't REQUIRE externals deps in root, add boost_headers (#265)

boost_headers is actually required for some distros apparently (notably
Arch, thanks username227 for spotting it), forces the bundled package
for it as well

AUR cpp-httplib also does not work with this for some reason, so in
order to support `CMAKE_DISABLE_FIND_PACKAGE_httplib` (required for
Arch if `cpp-httplib` is installed there), removes REQUIRED from the
external propagation calls (wasn't needed anyway idk why I added it)

I really wish we had more Arch developers tbh

Signed-off-by: crueter <crueter@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/265
Reviewed-by: Lizzie <lizzie@eden-emu.dev>

0 files changed, 0 insertions, 0 deletions