bootstrap: Fix libuv target platform conditions on macOS

In commit 714ce72882 (bootstrap: Make libuv available during bootstrap,
2017-09-13, v3.10.0-rc1~106^2) we modified libuv to use POSIX interfaces
during bootstrap.  However, some code still expects `TARGET_OS_IPHONE`
to be defined on Apple platforms to either `0` or `1`.  In order to
offer this, include `<TargetConditionals.h>` on Apple platforms even
when bootstrapping.
1 file changed