Add ANSI-C reserved words.

[jgornick]

ANSI C-keywords, as run thru the brain of R. Sonnenfeld
(www.nmt.edu/~rsonnenf)
and pulled from the web-site below
https://www.cheatography.com/ashlyn-black/cheat-sheets/c-reference/

auto
break
case
char
const
continue
default
do
double
else
enum
extern
float
for
goto
if
inline
int
long
register
restrict
return
short
signed
sizeof
static
struct
switch
typedef
union
unsigned
void
volatile
while

In addition to these, NEVER start a variable with an _underscore.
Many _words _with _LEADING _underscores are reserved for libraries and
compiler functions.

[jgornick]

Another reference: http://en.cppreference.com/w/c/keyword

Also, it brings up an interesting point that there are reserved words that are wildcards. For example, in C this is defined:

Also, each name that begins with a double underscore __ or an underscore followed by an uppercase letter is reserved: see identifier for details.