Not needed when only double is used.
Fixes the following warning: libavutil/avsscanf.c: In function 'decfloat': libavutil/avsscanf.c:354:9: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement] int bitlim = bits-3*(int)(rp-9); ^~~
Copied and adopted from musl implementation. * converted all 'long double' to 'double' * removed %m support