install.5 [ reading code ]

For the spirit of the LORD fills the world,
all-embracing, and knows what man says.
Wisdom 1:7

#if HAVE_SYS_WAIT_H
# include <sys/wait.h>
#endif

Implication. If p then q.
[math] { p \; \Rightarrow \; q } [/math]

If  HAVE_SYS_WAIT_H is true (nonzero value)
then compile the following line(compilation of #include <sys/wait.h>)
will be done.