Try checking in usr-host/bin for programs

They might be there if we've built them but haven't installed them
yet.  We need topBuilddir to be a global variable for this to work.

Also, use "nonnull splice" instead of "join" to slightly simplify
generating the list of paths to try.

Author: d-torrance

M2/Macaulay2/m2/programs.m2

@@ -89,18 +89,21 @@ findProgram(String, List) := opts -> (name, cmds) -> (
 	instance(opts.MinimumVersion, Sequence) and
 	class \ opts.MinimumVersion === (String, String)) then
 	error "expected MinimumVersion to be a sequence of two strings";
-    pathsToTry := fixPath \ join(
+    pathsToTry := fixPath \ nonnull flatten {
 	-- try user-configured path first
-	if programPaths#?name then {programPaths#name} else {},
+	if programPaths#?name then programPaths#name,
 	-- now try M2-installed path
-	{prefixDirectory | currentLayout#"programs"},
+	prefixDirectory | currentLayout#"programs",
 	-- any additional paths specified by the caller
-	opts.AdditionalPaths,
+	 opts.AdditionalPaths,
 	-- try PATH
-	if getenv "PATH" == "" then {} else apply(separate(":", getenv "PATH"),
+	if getenv "PATH" =!= "" then apply(
+	    separate(":", getenv "PATH"),
 	    dir -> if dir == "" then "." else dir),
 	-- try directory containing M2-binary
-	{bindir});
+	bindir,
+	-- try usr-host/bin
+	if topBuilddir =!= null then topBuilddir | "usr-host/bin"};
     prefixes := {(".*", "")} | opts.Prefix;
     errorCode := didNotFindProgram;
     versionFound := "0.0";

M2/Macaulay2/m2/startup.m2.in

@@ -40,7 +40,6 @@ if not firstTime then debug Core -- we need access to the private symbols (we re
 toString := value' getGlobalSymbol if firstTime then "simpleToString" else "toString"
 
 local exe
-local topBuilddir
 
 -- this next bit has to be *parsed* after the "debug" above, to prevent the symbols from being added to the User dictionary
 if firstTime then (