Rollup merge of rust-lang#24005 - ranma42:macosx-no-javac-popup, r=al…

…excrichton

MacOS X does not ship with Java installed by default. Instead it
includes binary stubs that upon execution pop up a message suggesting
the installation of the JDK.

Since `javac` is only used when `antlr4` is available, it is possible
to work around the popup by only probing for `javac` if `antlr4` has
been successfully detected (in which case the JDK is probably already
installed on the system).

Fixes rust-lang#23138.

configure

@@ -669,7 +669,6 @@ probe CFG_LD ld
 probe CFG_VALGRIND valgrind
 probe CFG_PERF perf
 probe CFG_ISCC iscc
-probe CFG_JAVAC javac
 probe CFG_ANTLR4 antlr4
 probe CFG_GRUN grun
 probe CFG_FLEX flex
@@ -679,6 +678,14 @@ probe CFG_XELATEX xelatex
 probe CFG_GDB gdb
 probe CFG_LLDB lldb
 
+# On MacOS X, invoking `javac` pops up a dialog if the JDK is not
+# installed. Since `javac` is only used if `antlr4` is available,
+# probe for it only in this case.
+if [ ! -z "$CFG_ANTLR4" ]
+then
+ probe CFG_JAVAC javac
+fi
+
 if [ ! -z "$CFG_GDB" ]
 then
  # Store GDB's version