libreboot-utils: simplify lbgetprogname

make it more reliable; it can't segfault
now, under any circumstance. not even
once.

the problem arised when lbsetname was not
called in a program, before calling the
function: lbgetprogname. a segfault would
occur, due to it being NULL.

not every os/libc has getprogname, so i have
my own implementation.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/libreboot-utils/README.md

@@ -31,7 +31,7 @@ of something like e.g. unveil, but in userspace!
 
 Mkhtemp is designed to be the most secure implementation
 possible, of mktemp, offering a heavy amount of hardening
-over traditional mktemp. Written in C89, and the plan is
+over traditional mktemp. Written in C99, and the plan is
 very much to keep this code portable over time - patches
 very much welcome.
 
@@ -241,7 +241,7 @@ a drop-in replacement on Linux distros (and BSDs if they
 want it), while providing a more hardened version and
 recommending that where possible.
 
-~~Rewrite it in rust~~ (nothing against it though, I just like C89 for some reason)
+~~Rewrite it in rust~~ (nothing against it though, I just like C99 for some reason)
 
 Also, generally document the history of mktemp, and how
 mkhtemp works in comparison.