[OS/2] nsinstall: Disable symlink options as they don't properly work.
[OS/2] security/nss/softoken: Port TEMP dir detection to OS/2.
[OS/2] Fix build break on GCC due to missing callconv.h.

callconv.h is missing from EMX, the Unicode stuff is defined in unidef.h.
More Telemetry code guarded with #ifdef MOZ_IPC.

Again, to build it on platforms that don't support IPC yet.