tests: Compile tested code with different CFLAGS for the tests
tests: Compile tested code with different CFLAGS for the tests

Some functions in glibc cannot be wrapped with the --wrap linker option,
because there are inlined when optimization options are used. Only with
-O0 and -Os this inlining does not happen. So the code under test is
compiled a second time just for the tests with -Os as the optimization
option.

cglindkamp/dfm