mkstemp.c:69:8: error: implicit declaration of function 'getpid' is invalid in C99 [-Werror,-Wimplicit-function-declaration] about zipruby HOT 4 OPEN

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/mikeboyd/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/gems/zipruby-0.3.6/ext
/Users/mikeboyd/.rbenv/versions/2.6.8/bin/ruby -I /Users/mikeboyd/.rbenv/versions/2.6.8/lib/ruby/2.6.0 -r ./siteconf20210812-27664-1wh21cw.rb extconf.rb -v\ 0.3.6\
--with-cflags\=-Wno-error\=implicit-function-declaration
checking for zlib.h... yes
checking for -lz... yes
checking for fseeko()... yes
checking for ftello()... yes
checking for mkstemp()... yes
creating Makefile

current directory: /Users/mikeboyd/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/gems/zipruby-0.3.6/ext
make "DESTDIR=" clean

current directory: /Users/mikeboyd/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/gems/zipruby-0.3.6/ext
make "DESTDIR="
compiling mkstemp.c
mkstemp.c:69:8: error: implicit declaration of function 'getpid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        pid = getpid();
              ^
1 error generated.
make: *** [mkstemp.o] Error 1

make failed, exit code 2

Gem files will remain installed in /Users/mikeboyd/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/gems/zipruby-0.3.6 for inspection.
Results logged to /Users/mikeboyd/.rbenv/versions/2.6.8/lib/ruby/gems/2.6.0/extensions/x86_64-darwin-20/2.6.0/zipruby-0.3.6/gem_make.out

An error occurred while installing zipruby (0.3.6), and Bundler cannot continue.
Make sure that `gem install zipruby -v '0.3.6' --source 'https://rubygems.org/'` succeeds before bundling.

In Gemfile:
  zipruby

gem install zipruby -v '0.3.6' -- --with-cflags="-Wno-error=implicit-function-declaration"