Improve detecting LLVM 3.5 from Homebrew

The main "llvm" Homebrew package is occasionally getting updated and is
not guaranteed to be version 3.5. Right now it's 3.6, but that depends
on the version of Homebrew that someone has installed.

This lists through all installed Homebrew packages named "llvm*" and
tests each `llvm-config --version` for "3.5*" until it finds one.

bin/ruby-build

@@ -812,12 +812,13 @@ require_llvm() {
   local llvm_version="$1"
   if [ "$(uname -s)" = "Darwin" ] && [ "$(osx_version)" -ge 1010 ]; then
     if [[ "$RUBY_CONFIGURE_OPTS" != *--llvm-* ]]; then
-      if [ "$llvm_version" = "3.2" ]; then
+      case "$llvm_version" in
+      3.2 )
         package_option ruby configure --prebuilt-name="llvm-3.2-x86_64-apple-darwin13.tar.bz2"
-      else
-        local llvm_prefix="$(brew --prefix llvm 2>/dev/null || true)"
-        local llvm_config="${llvm_prefix}/bin/llvm-config"
-        if [ -x "$llvm_config" ]; then
+        ;;
+      3.5 )
+        local llvm_config="$(locate_llvm "$llvm_version")"
+        if [ -n "$llvm_config" ]; then
           package_option ruby configure --llvm-config="$llvm_config"
         else
           { echo
@@ -833,11 +834,26 @@ require_llvm() {
           } >&3
           return 1
         fi
-      fi
+        ;;
+      esac
     fi
   fi
 }
 
+locate_llvm() {
+  local llvm_version="$1"
+  local package llvm_config
+  shopt -s nullglob
+  for package in `brew list 2>/dev/null | grep "^llvm"`; do
+    llvm_config="$(echo "$(brew --prefix "$package")/bin/llvm-config"*)"
+    if [ -n "$llvm_config" ] && [[ "$("$llvm_config" --version)" = "$llvm_version"* ]]; then
+      echo "$llvm_config"
+      break
+    fi
+  done
+  shopt -u nullglob
+}
+
 needs_yaml() {
   [[ "$RUBY_CONFIGURE_OPTS" != *--with-libyaml-dir=* ]] &&
   ! use_homebrew_yaml