Add a layer of macro indirection for long double files
which need to be built using another typename. Likewise,
add the L(num) macro used in a later patch to override
real constants.
These macros are only defined through the ldbl-128
math_ldbl.h header, thereby implicitly restricting
these macros to machines which back long double
with an IEEE binary128 format.
Likewise, appropriate changes are made for the few
files which indirectly include such ldbl-128 files.
These changes produce identical binaries for s390x,
aarch64, and ppc64.
There is quiet truncation to double arithmetic in several
files. I noticed them when building ldbl-128 in a
soft-fp context. This did not change any test results.
POSIX 2008 states that if the input for 'logb[f|l]' is a subnormal number
it should be treated as if it were normalized. This means the
implementation should calculate the log2 of the mantissa and add it to the
subnormal exponent (-126 for float and -1022 for double and IBM long
double). This patch takes care of that.
