(Esp. as building on Windows can put vital information into CFLAGS in LO's
configure.ac that needs to be passed down to external sub-builds, since
21250262 "Support universal C runtime, SDK 10
and .NET 4.6.")

Put the additional debug/optimization flags first, so that any CFLAGS passed
into the LO build can still override them.

Change-Id: I4aa43f8e65d7e32391acf8840d8e6159f33a4b79