RFR: JDK-8072023: Investigate and upgrade the minimum supported gnumake for JDK 9, from 3.81 to 4.0

[Erik Joelsson]

Please review this change to README-builds.html. I have updated all 
references to the GNU make version to specify that we recommend 4.0 or 
later on Windows. Cygwin has been shipping with 4.x for a long time now 
and we have been using it internally since the source code layout 
change. Using older versions of make, particularly 3.81 version commonly 
used for JDK 7, has been known to cause trouble with the JDK 9 (post src 
reshuffle) build. While 3.82.x versions probably still works in many 
cases, I would rather have us move to 4.x since there are features there 
we would eventually like to be able to use.

Bug: https://bugs.openjdk.java.net/browse/JDK-8072023
Patch:
diff -r d0321d15e0a0 README-builds.html
--- a/README-builds.html
+++ b/README-builds.html
@@ -41,7 +41,8 @@
                          The build is now a "<code>configure && 
make</code>" style build
                      </li>
                      <li>
-                        Any GNU make 3.81 or newer should work
+                        Any GNU make 3.81 or newer should work, except on
+                        Windows where 4.0 or newer is recommended.
                      </li>
                      <li>
                          The build should scale, i.e. more processors 
should
@@ -358,8 +359,8 @@
                  For all systems:
                  <ul>
                      <li>
-                        Be sure the GNU make utility is version 3.81 or 
newer,
-                        e.g. run "<code>make -version</code>"
+                        Be sure the GNU make utility is version 3.81 
(4.0 on
+                        windows) or newer, e.g. run "<code>make 
-version</code>"
                      </li>
                      <li>
                          Install a
@@ -1726,10 +1727,10 @@
              A few notes about using GNU make:
              <ul>
                  <li>
-                    You need GNU make version 3.81 or newer.
-                    If the GNU make utility on your systems is not
-                    3.81 or newer,
-                    see <a href="#buildgmake">"Building GNU make"</a>.
+                    You need GNU make version 3.81 or newer. On Windows 
4.0 or
+                    newer is recommended.
+                    If the GNU make utility on your systems is not of a 
suitable
+                    version see <a href="#buildgmake">"Building GNU 
make"</a>.
                  </li>
                  <li>
                      Place the location of the GNU make binary in the


/Erik