Ubuntu 18.04 build assumptions

[DanRStevens]

Not a bug, though I wanted to open this to make these errors searchable. Perhaps they might lead to documentation updates.

The following packages were needed to build on Ubuntu 18.04:

• build-essential
• libx11-dev
• gawk

---

If the libx11-dev package is not installed, make will fail with:

/bin/bash ./libxlibtrace-atoms.c.sh
cat: /usr/include/X11/Xatom.h: No such file or directory

---

If gawk is not installed, then make will fail with:

/bin/bash ./libxlibtrace-functions.h.sh
awk: line 88: regular expression compile failed (missing '(')
^)[ ]*;$
awk: line 21: function gensub never defined
awk: line 21: function gensub never defined
awk: line 21: function gensub never defined
Makefile:623: recipe for target 'libxlibtrace-functions.h' failed

It seems there is a slightly incompatible version of awk that is installed by default on Ubuntu. The gensub function is an extension specific to GNU awk.

Documentation:
https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html

Those functions that are specific to gawk are marked with a pound sign (‘#’). They are not available in compatibility mode (see section Command-Line Options)
...
gensub(regexp, replacement, how [, target]) #