csu: Fix .eh_frame_hdr errors seen on i386

csu: Fix .eh_frame_hdr errors seen on i386

The libcsu object files should have been generated with
-fno-asynchronous-unwind-tables.  The crtbegin*, crtend* objects,
specific to a compiler, were generated with this flag on both platforms
as seen in the vendor build.  This commit builds libcsu with the same
cflags on both platforms, and it allows the error frame header to get
built successfully.

This has been seen on i386 for a while, and later bug #2511 hit upon
it outside of the world build.