Rather than setting them in the build profile, just set them in
etc/defaults.conf (overridable via etc/conf) to simplify the code.
- Also enable _FORTIFY_SOURCE=2 in CPPFLAGS.
- Also enable -z,relro in LDFLAGS.
As suggested by @chneukirchen.
glibc uses the cross compiler preprocessor to know what architecture
to compile for, resulting in wrong architecture being used with the armv6
cross compiler.
