Add C++ Guards

[code2828]

Fully tested.
Output:

libtool --mode=compile --tag=CC cc -I. -Wall -std=c99 -O2  -o t/static_xterm.lo -c t/static_xterm.c
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_xterm.c  -fPIC -DPIC -o t/.libs/static_xterm.o
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_xterm.c -o t/static_xterm.o >/dev/null 2>&1
libtool --mode=link --tag=CC cc  -o t/static_xterm.t libunibilium.la t/static_xterm.lo
^Cmake: *** [Makefile:81: t/static_xterm.t] Interrupt
make: *** Deleting intermediate file 't/static_xterm.lo'

gitpod /workspace/unibilium $ make test -j8
libtool --mode=compile --tag=CC cc -I. -Wall -std=c99 -O2  -o t/static_xterm.lo -c t/static_xterm.c
libtool --mode=compile --tag=CC cc -I. -Wall -std=c99 -O2  -o t/static_tmux.lo -c t/static_tmux.c
libtool --mode=compile --tag=CC cc -I. -Wall -std=c99 -O2  -o t/wide-format.lo -c t/wide-format.c
libtool --mode=compile --tag=CC cc -I. -Wall -std=c99 -O2  -o t/if-then-else.lo -c t/if-then-else.c
libtool --mode=compile --tag=CC cc -I. -Wall -std=c99 -O2  -o t/static_screen.lo -c t/static_screen.c
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_xterm.c  -fPIC -DPIC -o t/.libs/static_xterm.o
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_screen.c  -fPIC -DPIC -o t/.libs/static_screen.o
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/wide-format.c  -fPIC -DPIC -o t/.libs/wide-format.o
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/if-then-else.c  -fPIC -DPIC -o t/.libs/if-then-else.o
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_tmux.c  -fPIC -DPIC -o t/.libs/static_tmux.o
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/wide-format.c -o t/wide-format.o >/dev/null 2>&1
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/if-then-else.c -o t/if-then-else.o >/dev/null 2>&1
libtool --mode=link --tag=CC cc  -o t/wide-format.t libunibilium.la t/wide-format.lo
libtool --mode=link --tag=CC cc  -o t/if-then-else.t libunibilium.la t/if-then-else.lo
libtool: link: cc -o t/.libs/wide-format.t t/.libs/wide-format.o  ./.libs/libunibilium.so 
libtool: link: cc -o t/.libs/if-then-else.t t/.libs/if-then-else.o  ./.libs/libunibilium.so 
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_screen.c -o t/static_screen.o >/dev/null 2>&1
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_xterm.c -o t/static_xterm.o >/dev/null 2>&1
libtool: compile:  cc -I. -Wall -std=c99 -O2 -c t/static_tmux.c -o t/static_tmux.o >/dev/null 2>&1
libtool --mode=link --tag=CC cc  -o t/static_screen.t libunibilium.la t/static_screen.lo
libtool: link: cc -o t/.libs/static_screen.t t/.libs/static_screen.o  ./.libs/libunibilium.so 
libtool --mode=link --tag=CC cc  -o t/static_xterm.t libunibilium.la t/static_xterm.lo
libtool: link: cc -o t/.libs/static_xterm.t t/.libs/static_xterm.o  ./.libs/libunibilium.so 
libtool --mode=link --tag=CC cc  -o t/static_tmux.t libunibilium.la t/static_tmux.lo
libtool: link: cc -o t/.libs/static_tmux.t t/.libs/static_tmux.o  ./.libs/libunibilium.so 
prove -j8
t/00_load.t ................. ok                                        
t/if-then-else.t ............ ok                                        
t/wide-format.t ............. ok                                        
t/static_screen-256color.t .. ok                                        
t/static_screen.t ........... ok                                        
t/static_tmux.t ............. ok                                        
t/static_xterm-256color.t ... ok                                        
t/static_xterm.t ............ ok       
All tests successful.
Files=8, Tests=3137,  0 wallclock secs ( 0.25 usr  0.02 sys +  0.24 cusr  0.36 csys =  0.87 CPU)
Result: PASS
rm t/wide-format.lo t/static_xterm.lo t/static_screen.lo t/if-then-else.lo t/static_tmux.lo