Fix the fact that previously strtof/d/ld would only accept a NaN as
having parentheses if the thing in the parentheses was a valid number,
now it will accept any combination of letters and numbers, but will only
put valid numbers in the mantissa.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D113790

Update binaryExpTofloat so that it will round correctly for long inputs when converting hexadecimal strings to floating points.

Differential Revision: https://reviews.llvm.org/D113815

Combine two loops in decimalStringToFloat and hexadecimalStringToFloat that extract the digits and re-arrange them a little bit.  This slightly improves the performance of strtof and strtod:
Running libc_str_to_float_comparison_test parse-number-fxx-test_data/data/* on my machine (Ryzen 1700)
- with glibc: ~1.92 seconds
- with current implementation: ~1.78 seconds
- with this change: ~1.67 seconds

Differential Revision: https://reviews.llvm.org/D113681

When strtof/d/ld return a subnormal number they may set errno to
ERANGE. This change makes this behavior more consistent by making any
decimal number converting to a subnormal set errno to ERANGE. This
brings it in line with hexadecimals, which currently only set errno to
ERANGE if the number is truncated when converting to a subnormal.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D113626

Add quietNaNMask consts to FloatProperties and make LongDoubleBitsX86
clear the extra bits that aren't set when initializing with an 80 bit
long double.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D113625

Split the code for parsing hexadecimal floating point numbers from the
code for parsing the decimal floating point numbers so that the parsing
can be faster for both of them.

This decreases the time for the benchmark in release mode by about 15%,
which noticeably beats GLibc.

Old version: 2.299s
New version: 1.893s
GLibc: 2.133s

Tests run by running the following command 10 times for each version:
time ~/llvm-project/build/bin/libc_str_to_float_comparison_test ~/parse-number-fxx-test-data/data/*

the parse-number-fxx-test-data-repository is here:
https://github.com/nigeltao/parse-number-fxx-test-data/tree/fe94de252c691900982050c8e7c503d1efd1299a

It's important to build llvm-libc in Release mode for accurate
performance comparisons against glibc (set -DCMAKE_BUILD_TYPE=Release in
your cmake).
You also have to build the libc_str_to_float_comparison_test target.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D113036

Adds an implementation for stpcpy and stpncpy, which are posix extension
functions.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D111913

This allows shipping individual functions without also having to provide
memset or bzero at the expense of bigger functions.

Similar to D113097.

Differential Revision: https://reviews.llvm.org/D113108