Fix arm64 fenv warnings, and make warnings errors.

Fix arm64 fenv warnings, and make warnings errors.

Even though the control registers being read/written in fenv.c only
have 32 bits that are used, the instructions take a 64 bit register.
Make sure the inline assembler in the macros use 64 bit values.

Verified that before the change and after the change, the disassembly
is exactly the same.

In addition, add -Werror to the cflags.

Change-Id: I6603779327488c23e3aab13300edf2e02b101916