[Cfp-interest 2665] incorrect example H.12.2p4

[Vincent Lefevre]

The example in H.12.2p4

#define __STDC_WANT_IEC_60559_TYPES_EXT__
#include <stdlib.h>
#define MAXSIZE 41 // > intermediate hex string length
unsigned char b128[16]; // for input binary128 datum
_Decimal128 d128; // for result
char s[MAXSIZE];
// store input binary128 datum in array b128
...
strfromencf128(s, MAXSIZE, "%a", b128);
d128 = strtod128(s, NULL);
...

assumes that decimal-point takes only 1 byte. But this might not
be true in some locales. I don't know whether this has already
been seen in real locales, but it is known that thousands_sep
can take several bytes in practice, e.g. with "fr_FR.utf8":
https://reviews.llvm.org/D27167 says that thousands_sep is U+00A0
on FreeBSD 11. And on Linux, it is U+202F NARROW NO-BREAK SPACE,
i.e. the string e2 80 af (3 bytes).

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