Brought over several improvements from the jit branch.

[pbtoast]

• The build system now uses the lld or the gold linker if available.
• Loggers don't close system file descriptors when their streams are set.
• Added log_flush(), which manually flushes a log stream.
• The installation tree is now searched for dynamic load libraries.
• Added a lua dl module to expose dynamic load library paths.
• Minor cleanup and lua test coverage improvements.

[codecov[bot]]

Codecov Report

Merging #344 into master will increase coverage by 0.02%. The diff coverage is 56.66%.

@@            Coverage Diff             @@
##           master     #344      +/-   ##
==========================================
+ Coverage   80.63%   80.65%   +0.02%     
==========================================
  Files         243      243              
  Lines       37926    37952      +26     
==========================================
+ Hits        30581    30612      +31     
+ Misses       7345     7340       -5

Impacted Files	Coverage Δ
core/polymec.c	65.25% <100%> (+0.75%)	:arrow_up:
core/logging.c	89.67% <37.5%> (-1.11%)	:arrow_down:
core/lua_core.c	79.09% <57.89%> (+0.42%)	:arrow_up:
core/lua_types.c	88.97% <0%> (+0.78%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 730933b...7288c28. Read the comment docs.

[codecov[bot]]

Codecov Report

Merging #344 into master will increase coverage by 0.02%. The diff coverage is 56.66%.

@@            Coverage Diff             @@
##           master     #344      +/-   ##
==========================================
+ Coverage   80.63%   80.65%   +0.02%     
==========================================
  Files         243      243              
  Lines       37926    37952      +26     
==========================================
+ Hits        30581    30612      +31     
+ Misses       7345     7340       -5

Impacted Files	Coverage Δ
core/polymec.c	65.25% <100%> (+0.75%)	:arrow_up:
core/logging.c	89.67% <37.5%> (-1.11%)	:arrow_down:
core/lua_core.c	79.09% <57.89%> (+0.42%)	:arrow_up:
core/lua_types.c	88.97% <0%> (+0.78%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 730933b...7288c28. Read the comment docs.