crosstool-ng: update caveats and specify tool paths

Closes Homebrew/homebrew#20140.
Closes Homebrew/homebrew#20223.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/crosstool-ng.rb

@@ -29,12 +29,19 @@ class CrosstoolNg < Formula
                           "--with-libtool=glibtool",
                           "--with-libtoolize=glibtoolize",
                           "--with-install=ginstall",
+                          "--with-sed=gsed",
+                          "--with-awk=gawk",
                           "CFLAGS=-std=gnu89"
     # Must be done in two steps
     system "make"
     system "make install"
   end
 
+  def caveats; <<-EOS.undent
+    You will need to install modern gcc compiler in order to use this tool.
+    EOS
+  end
+
   test do
     system "#{bin}/ct-ng", "version"
   end