Make compiler built in libraries dynamic

[suoto]

Moving suoto/vim-hdl#4 to hdlcc.

Built-in libraries are statically defined, which means that things will break on different environments. We can either use the compiler to get them somehow or create an option for the user to set manually. Using the compiler is the preferred approach.

[suoto]

ModelSim shows configured libraries by calling vmap without parameters:

Reading /opt/modelsim/modelsim_dlx/linuxpe/../modelsim.ini
"std" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../std.
"ieee" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../ieee.
"vital2000" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../vital2000.
"verilog" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../verilog.
"std_developerskit" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../std_developerskit.
"synopsys" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../synopsys.
"modelsim_lib" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../modelsim_lib.
"sv_std" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../sv_std.
"floatfixlib" maps to directory /opt/modelsim/modelsim_dlx/linuxpe/../floatfixlib.
"simprim" maps to directory /opt/Xilinx/13.4/ISE_DS/ISE/vhdl/mti_se/10.1a/lin64/simprim/.
"unisim" maps to directory /opt/Xilinx/13.4/ISE_DS/ISE/vhdl/mti_se/10.1a/lin64/unisim.
"xilinxcorelib" maps to directory /opt/Xilinx/13.4/ISE_DS/ISE/vhdl/mti_se/10.1a/lin64/xilinxcorelib/.
"unimacro" maps to directory /opt/Xilinx/13.4/ISE_DS/ISE/vhdl/mti_se/10.1a/lin64/unimacro/.
"cpld" maps to directory /opt/Xilinx/13.4/ISE_DS/ISE/vhdl/mti_se/10.1a/lin64/cpld.

Similarly, GHDL displays via ghdl --dispconfig:

$ ghdl --dispconfig
command line prefix (--PREFIX): (not set)
environment prefix (GHDL_PREFIX): (not set)
exec prefix (from program name): /home/asouto/.local

library prefix: /home/asouto/.local/lib/ghdl
library directory: /home/asouto/.local/lib/ghdl
command_name: ghdl
default library pathes:
 /home/asouto/.local/lib/ghdl/v93/std/
 /home/asouto/.local/lib/ghdl/v93/ieee/

There outputs can be parsed and cached when creating the builder object.

[suoto]

Issue was fixed.