POSIX says:
"If ptr is a null pointer, realloc() shall be equivalent to malloc() for the
 specified size."

Current font caching algorithm contains a use after free error. A font
removed from `frc` might be still listed in `wx.specbuf`. It will lead
to a crash inside `XftDrawGlyphFontSpec()`.

Steps to reproduce:
$ st -f 'Misc Tamsyn:scalable=false'
$ curl https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt

Of course, result depends on fonts installed on a system and fontconfig.
In my case, I'm getting consistent segfaults with different fonts.

I replaced a fixed array with a simple unbounded buffer with a constant
growth rate. Cache starts with a capacity of 0, gets increments by 16,
and never shrinks. On my machine after `cat UTF-8-demo.txt` buffer
reaches a capacity of 192. During casual use capacity stays at 0.

Features:

- Allow input methods swap with hotkey (E.g. left ctrl + left shift).
- Over-the-spot pre-editing style, pre-edit data placed over insertion point.
- Restart IME without segmentation fault.

TODO:

- Automatically pickup IME if st started before IME

This was changed before in:
commit 20f713548d on Wed Jan 25 19:17:38 2017

This complements the work done in d4928ed, allowing the user to specify
the preprocessor flags with the CPPFLAGS environment variable. This is
useful for example to specify preprocessor macros with -D.

CFLAGS could be used instead, but CPPFLAGS is more correct and is expected
to be honored in some cases. For example, the helper scripts to build
Debian packages make use of CPPFLAGS, but the variable is currently
being ignored unless manually appended to CFLAGS.

In this way the path of pkg-config can be overridden from the command
line. This is useful for example when cross-compiling.

patch by Younes Khoudli (changed slightly). Thanks

reported by Avi Halachmi (:avih)" <avihpit@yahoo.com>

patch slightly changed by me.

And move it to the patches section.
Keeping it would force to add an exec pledge on OpenBSD, and some
people think it's bloated, so bye!

This reverts commit 1911c9274d.

This reverts commit b51bcd5553.

This reverts commit 5535c1f04c.

Reported-by: Ivan Tham <pickfire@riseup.net>

Prevent to realloc xw.specbuc with a negative number of col.
Add proper hints for the minimal size, for one character.

feedback from Klemens, thanks

"restore the old behaviour that the primary doesn't get deleted by a simple
left click"

Patch by Daniel Tameling <tamelingdaniel@gmail.com>, thanks!

on some platforms (OpenBSD) this changes the exposed argv in tools using
the kvm_* interface, such as ps and pgrep.

Simplifies logic in a couple places and removes a redundant function
call.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

When possible, declare functions/variables static and move struct
definitions out of headers.  In order to allow utf8decode to become
internal, use codepoint for DECSCUSR extension directly.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

Prefer passing arguments to declaring external global variables.  The
only remaining usage of extern is for config.h variables which are
needed in st.c instead of x.c (where it is now included).

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

The xinit function only needs to the rows/cols, so pass those in rather
than accessing term directly.  With a bit of arithmetic, we are able to
avoid the need for term.row and term.col in x2col, y2row, and
xdrawglyphfontspecs as well, completing the removal.

Term is now fully internal to st.c.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

Gradually reducing x.c dependency on Term object.  Old and new cursor
glyph/position are passed to xdrawcursor.  (There may be an opportunity
to refactor further if we can unify "clear old cursor" and "draw new
cursor" functionality.)

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

Introduces three functions to encapsulate X-specific behavior:
 * xdrawline: draws a portion of a single line (used by drawregion)
 * xbegindraw: called to prepare for drawing (will be useful for e.g.
   Wayland) and returns true if drawing should happen
 * xfinishdraw: called to finish drawing (used by draw)

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>