Wrap dotu from BLAS and rename dot to dotc for complex.
add entries to helpdb & news.md for minmax and extrema
Merge pull request #5285 from lindahua/dh/minmax_doc

add entries to helpdb & news.md for minmax and extrema
Corrected position for entry for minmax & extrema in NEWS.md
revert the edit on helpdb.jl
Merge pull request #5287 from lindahua/dh/minmax_doc2

revert the edit on helpdb.jl
Use nnz to implement sum over bool arrays

This minor change results in about 1.5x - 2x speedup and smaller memory footprint.
Merge pull request #5288 from lindahua/dh/sumbool

Use nnz to implement sum over bool arrays
Merge pull request #5283 from JuliaLang/anj/dotu

Wrap dotu from BLAS and rename dot to dotc for complex.
fix #5286, give an error for Void/None as a ccall argument type
Fix \{A::Triangular,b} test

Use ideal perturbation bound for roundoff analysis of Gaussian
elimination. (Golub and Van Loan, Matrix Computations, 3/e, Section 3.3,
Eq. 3.3.2, p105)

Closes #5278
Do not add PREFIX to LIBDIR, and make it relative to BUILD

LIBDIR is supposed to be an absolute path, already
including PREFIX. Also fix a few places where 'lib'
was still hardcoded.
Do not add PREFIX to SYSCONFDIR, and make it relative to BUILD

Remove special-cases testing whether SYSCONFDIR is set:
giving it a default value is enough.
Adapt relative RPATH and path to sys.ji to LIBDIR

Since now LIBDIR can point to anywhere, and not only to a directory
immediately under PREFIX, it is not guaranteed that $(ORIGIN)/../$(JL_LIBDIR)
points to $(JL_LIBDIR).
Add BINDIR, LIBEXECDIR, DATADIR and INCLUDEDIR

These are needed to get the same directory layout under BUILD as after
installation under DESTDIR and eventually PREFIX.
Use empty PREFIX by default

By using an empty PREFIX and BUILD=usr/, the tree
structure remains the same by default as before. This
means dependencies do not have to be rebuilt.
Fix path to libuv .h files
Remove potential duplicate target directories

The old code was cheking manually for duplicates which typically
arose on Windows. Better do that reliably (anyway it does not work
now that paths are absolute).
Use standard lowercase directory names

Change PREFIX, BINDIR, LIBDIR, LIBEXECDIR, INCLUDEDIR and SYSCONFDIR to
lowercase as is standard. Rename DATADIR to datarootdir for correctness.
Replace JL_LIBDIR with libdir as they are the same everywhere.
Override directory env vars for deps Makefile

Now that we use standard names such as 'prefix', if the top-level
Makefile is called with such environment variables set, they will be
passed as-is to dependencies, overriding what is passed to ./configure.