`is_nan_or_inf` gives warning with `-Wall -Wextra`.

[theNoof]

compiling a simple program containing jim2.h with the -Wall -Wextra flags, you get this warning:

gcc src/main.c -o target/ndoc -O3 -Wall -Wextra -ggdb
In file included from src/main.c:2:
src/../external/jim2.h: In function ‘is_nan_or_inf’:
src/../external/jim2.h:214:16: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  214 |     return (((*(unsigned long long int*) &x) >> 52ULL) & mask) == mask;
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

(output from the makefile of my project.)

i've tried to google alround for a quick minute and find a solution, but didnt find anything.

for poeple compiling with -Werror, thats a problem. otherwise its just an inconvinience.