[opam] Enable user opam switch named differently than compiler

Summary:
Currently only user-specified opam switches that name compilers are
supported. This diff generalizes this so that the switch name and
compiler can be specified separately.

Reviewed By: jvillard

Differential Revision: D18477910

fbshipit-source-id: f17c6363d

build-infer.sh

@@ -121,7 +121,7 @@ fi
 
 setup_opam () {
     opam var root 1>/dev/null 2>/dev/null || opam init --reinit --bare --no-setup
-    opam_switch_create_if_needed "$INFER_OPAM_SWITCH"
+    opam_switch_create_if_needed "$INFER_OPAM_SWITCH" "$INFER_OPAM_COMPILER"
     opam switch set "$INFER_OPAM_SWITCH"
 }
 

scripts/opam_utils.sh

@@ -50,6 +50,7 @@ opam_require_version_2 () {
 # assumes opam is available and initialized
 opam_switch_create_if_needed () {
     local switch=$1
+    local compiler=$2
     local switch_exists=no
     for installed_switch in $(opam switch list --short); do
         if [ "$installed_switch" == "$switch" ]; then
@@ -58,7 +59,7 @@ opam_switch_create_if_needed () {
         fi
     done
     if [ "$switch_exists" = "no" ]; then
-        opam switch create "$switch"
+        opam switch create "$switch" "$compiler"
     fi
 }