Update Cabal submodule to HEAD (1.21)

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Set i686 as the minimum architecture on 32-bit mingw

Signed-off-by: Austin Seipp <austin@well-typed.com>
travis: Install process via cabal

and install to global data base (bad practice, but ok on a throw-away CI
system).
Document OVERLAP pragmas.
Documentation typo
Comments only
Revert "Update Cabal submodule to HEAD (1.21)"

This reverts commit af28e61c7e84b8eb89fdfd9671af83a2a13f554a.
We'll wait until it's possible to bootstrap from 7.6 out of the box.
ghci: detabify/dewhitespace RtClosureInspect

Signed-off-by: Austin Seipp <austin@well-typed.com>
parser: detabify/dewhitespace Ctype

Signed-off-by: Austin Seipp <austin@well-typed.com>
parser: detabify/dewhitespace cutils.c

Signed-off-by: Austin Seipp <austin@well-typed.com>
profiling: detabify/unwhitespace CostCentre

Signed-off-by: Austin Seipp <austin@well-typed.com>
cmm: detabify/unwhitespace CmmInfo

Signed-off-by: Austin Seipp <austin@well-typed.com>
cmm: detabify/unwhitespace CmmLex

Signed-off-by: Austin Seipp <austin@well-typed.com>
ghci: detabify/unwhitespace ByteCodeGen

Signed-off-by: Austin Seipp <austin@well-typed.com>
ghci: detabify/unwhitespace ByteCodeInstr

Signed-off-by: Austin Seipp <austin@well-typed.com>
main: detabify/unwhitespace PprTyThing

Signed-off-by: Austin Seipp <austin@well-typed.com>
prelude: detabify/unwhitespace PrelInfo

Signed-off-by: Austin Seipp <austin@well-typed.com>
nativeGen: detabify/dewhitespace Size

Signed-off-by: Austin Seipp <austin@well-typed.com>
nativeGen: detabify/dewhitespace Reg

Signed-off-by: Austin Seipp <austin@well-typed.com>
nativeGen: detabify/dewhitespace X86/RegInfo

Signed-off-by: Austin Seipp <austin@well-typed.com>