This is a preparatory patch to enable building a _Float128
variant to ease reuse when building a _Float128 variant to
alias this long double only symbol.
Notably, stubs are added where missing to the native _Float128
sysdep dir to prevent building these newly templated variants
created inside the build directories.
Also noteworthy are the changes around LIBM_SVID_COMPAT. These
changes are not intuitive. The templated version is only
enabled when !LIBM_SVID_COMPAT, and the compat version is
predicated entirely on LIBM_SVID_COMPAT. Thus, exactly one is
stubbed out entirely when building. The nldbl scalb compat
files are updated to account for this.
Likewise, fixup the reuse of m68k's e_scalb{f,l}.c to include
it's override of e_scalb.c. Otherwise, the search path finds
the templated copy in the build directory. This could be
futher simplified by providing an overridden template, but I
lack the hardware to verify.
