patch by Pascal Cuoq (with minor tweaks to comments)

this was the cause of crashes in printf when attempting to print
floating point values.

1. my interpretation of subject sequence definition was wrong. adjust
parser to conform to the standard.

2. some code for handling tail overflow case was missing (forgot to
finish writing it).

3. typo (= instead of ==) caused ERANGE to wrongly behave like EINVAL

stopping without letting the parser see a stop character prevented
getting a result. so treat all high chars as the null character and
pass them into the parser.

also eliminated ugly tmp var using compound literals.

this fixes a number of bugs in integer parsing due to lazy haphazard
wrapping, as well as some misinterpretations of the standard. the new
parser is able to work character-at-a-time or on whole strings, making
it easy to support the wide functions without unbounded space for
conversion. it will also be possible to update scanf to use the new
parser.

Smoothsort is an adaptive variant of heapsort. This version was
written by Valentin Ochs (apo) specifically for inclusion in musl. I
worked with him to get it working in O(1) memory usage even with giant
array element widths, and to optimize it heavily for size and speed.
It's still roughly 4 times as large as the old heap sort
implementation, but roughly 20 times faster given an almost-sorted
array of 1M elements (20 being the base-2 log of 1M), i.e. it really
does reduce O(n log n) to O(n) in the mostly-sorted case. It's still
somewhat slower than glibc's Introsort for random input, but now
considerably faster than glibc when the input is already sorted, or
mostly sorted.

0e10000000000000000000000000000000 was setting ERANGE

exponent char e/p was considered part of the match even if not
followed by a valid decimal value

"1e +10" was parsed as "1e+10"

hex digits were misinterpreted as 0..5 instead of 10..15

sadly the C language does not specify any such implicit conversion, so
this is not a matter of just fixing warnings (as gcc treats it) but
actual errors. i would like to revisit a number of these changes and
possibly revise the types used to reduce the number of casts required.

this is actually a workaround for a bug in gcc, whereby it asserts
inequality of the keys being compared...