Revert "Travis: Use GHC 8.6.1"

This reverts commit 3da6e7cd.

.travis.yml

 # This Travis job script has been generated by a script via
 #
-#   runghc make_travis_yml_2.hs '-o' '.travis.yml' '--ghc-head' '--no-unconstrained' 'cabal.project'
+#   runghc make_travis_yml_2.hs '-o' '.travis.yml' '--ghc-head' '--no-installed' 'cabal.project'
 #
 # For more information, see https://github.com/hvr/multi-ghc-travis
 #
@@ -28,9 +28,6 @@ before_cache:
 
 matrix:
   include:
-    - compiler: "ghc-8.6.1"
-      env: GHCHEAD=true
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-8.6.1], sources: [hvr-ghc]}}
     - compiler: "ghc-8.4.3"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-8.4.3], sources: [hvr-ghc]}}
@@ -94,7 +91,6 @@ matrix:
 
   allow_failures:
     - compiler: "ghc-head"
-    - compiler: "ghc-8.6.1"
 
 before_install:
   - HC=${CC}
@@ -112,8 +108,7 @@ install:
   - BENCH=${BENCH---enable-benchmarks}
   - TEST=${TEST---enable-tests}
   - HADDOCK=${HADDOCK-true}
-  - UNCONSTRAINED=${UNCONSTRAINED-true}
-  - NOINSTALLEDCONSTRAINTS=${NOINSTALLEDCONSTRAINTS-false}
+  - INSTALLED=${INSTALLED-true}
   - GHCHEAD=${GHCHEAD-false}
   - travis_retry cabal update -v
   - "sed -i.bak 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config"
@@ -121,8 +116,7 @@ install:
   # Overlay Hackage Package Index for GHC HEAD: https://github.com/hvr/head.hackage
   - |
     if $GHCHEAD; then
-      sed -i 's/-- allow-newer: .*/allow-newer: *:base/' ${HOME}/.cabal/config
-      for pkg in $($HCPKG list --simple-output); do pkg=$(echo $pkg | sed 's/-[^-]*$//'); sed -i "s/allow-newer: /allow-newer: *:$pkg, /" ${HOME}/.cabal/config; done
+      sed -i.bak 's/-- allow-newer:.*/allow-newer: *:base, *:template-haskell, *:ghc, *:Cabal/' ${HOME}/.cabal/config
 
       echo 'repository head.hackage'                                                        >> ${HOME}/.cabal/config
       echo '   url: http://head.hackage.haskell.org/'                                       >> ${HOME}/.cabal/config
@@ -132,16 +126,11 @@ install:
       echo '              8f79fd2389ab2967354407ec852cbe73f2e8635793ac446d09461ffb99527f6e' >> ${HOME}/.cabal/config
       echo '   key-threshold: 3'                                                            >> ${HOME}/.cabal.config
 
-      grep -Ev -- '^\s*--' ${HOME}/.cabal/config | grep -Ev '^\s*$'
-
       cabal new-update head.hackage -v
     fi
   - grep -Ev -- '^\s*--' ${HOME}/.cabal/config | grep -Ev '^\s*$'
   - "printf 'packages: \".\"\\n' > cabal.project"
-  - touch cabal.project.local
-  - "if ! $NOINSTALLEDCONSTRAINTS; then for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/^/constraints: /' | sed 's/-[^-]*$/ installed/' >> cabal.project.local; done; fi"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
+  - cat cabal.project
   - if [ -f "./configure.ac" ]; then
       (cd "." && autoreconf -i);
     fi
@@ -160,13 +149,11 @@ script:
   - cd ${DISTDIR} || false
   - find . -maxdepth 1 -name '*.tar.gz' -exec tar -xvf '{}' \;
   - "printf 'packages: unix-*/*.cabal\\n' > cabal.project"
-  - touch cabal.project.local
-  - "if ! $NOINSTALLEDCONSTRAINTS; then for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/^/constraints: /' | sed 's/-[^-]*$/ installed/' >> cabal.project.local; done; fi"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
+  - cat cabal.project
   # this builds all libraries and executables (without tests/benchmarks)
   - cabal new-build -w ${HC} --disable-tests --disable-benchmarks all
 
+
   # build & run tests, build benchmarks
   - cabal new-build -w ${HC} ${TEST} ${BENCH} all
 
@@ -177,5 +164,5 @@ script:
   - rm -rf ./dist-newstyle
   - if $HADDOCK; then cabal new-haddock -w ${HC} ${TEST} ${BENCH} all; else echo "Skipping haddock generation";fi
 
-# REGENDATA ["-o",".travis.yml","--ghc-head","--no-unconstrained","cabal.project"]
+# REGENDATA ["-o",".travis.yml","--ghc-head","--no-installed","cabal.project"]
 # EOF

unix.cabal

@@ -11,8 +11,7 @@ bug-reports:    https://github.com/haskell/unix/issues
 synopsis:       POSIX functionality
 category:       System
 build-type:     Configure
-tested-with:    GHC==8.6.1,
-                GHC==8.4.3, GHC==8.4.2, GHC==8.4.1,
+tested-with:    GHC==8.4.3, GHC==8.4.2, GHC==8.4.1,
                 GHC==8.2.2, GHC==8.2.1,
                 GHC==8.0.2, GHC==8.0.1,
                 GHC==7.10.3, GHC==7.10.2, GHC==7.10.1,