fix #6599
better fix for #6566. also increase inlining

this inlining threshold seems to translates to approximately 8
expressions of low complexity, and about the same number of llvm instructions
incorporate Jeff's comments for inlining patch
etree should use integers, not floating point

A thinko on my part in the previous version.  I confused `Tv` and `Ti`.
fix #6634, bug where a type decl requires a captured variable
Only set LIBLAPACK if not provided by the ENV

liblapack ist not always called liblapack in the system but different implementations have different names. Only set them to the default if the names were not declared yet (i.e. do the same as we do already with LIBBLASNAME).
Speed up symbol lookup by using hash has major key.
Merge branch 'jn/6599'
Merge pull request #6636 from JuliaLang/db/etree

etree should use integers, not floating point
More detailed explanation of cases where @simd is likely to help (#5355).
Merge branch 'master' of github.com:JuliaLang/julia
Merge pull request #6640 from xhochy/patch-3

Only set LIBLAPACK if not provided by the ENV
Start out LLVM_FLAGS with += so that options can be provided in Make.user
Also add --enable-keep-symbols --enable-debug-symbols when doing `make LLVM_DEBUG=1`
As discussed in #6639.
fix #6651, use promotion in clamp()
Merge pull request #6644 from ArchRobison/adr/fastsym

Speed up symbol lookup by using hash code as major key.
fix #6653
better regression test for #6653