Document need to clear MAKELEVEL when invoking PG build from a makefile.

Since commit 3b8f6e75f, failure to do this would lead to
submake-generated-headers not doing anything, so that references to
generated or symlinked headers would fail.  Previous to that, the
omission only led to temp-install not doing anything, which apparently
affects many fewer people (doesn't anybody use "make check" in their
build rules??).  Hence, backpatch to v11 but not further.

Per complaints from Christoph Berg, Jakob Egger, and others.

diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index fa90e9104aea41a8f7d5a8ea8754d656df2e3255..a88cd21f453112b419c89e9f77fcff3e4b74b9da 100644 (file)
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -1599,12 +1599,13 @@ su - postgres
    Build
 
    
-    To start the build, type:
+    To start the build, type either of:
 
 make
+make all
 
-    (Remember to use GNU make.) The build
-    will take a few minutes depending on your
+    (Remember to use GNU make.)
+    The build will take a few minutes depending on your
     hardware. The last line displayed should be:
 
 All of PostgreSQL successfully made. Ready to install.
@@ -1623,6 +1624,18 @@ All of PostgreSQL successfully made. Ready to install.
 PostgreSQL, contrib, and documentation successfully made. Ready to install.
 
    
+
+   
+    If you want to invoke the build from another makefile rather than
+    manually, you must unset MAKELEVEL or set it to zero,
+    for instance like this:
+
+build-postgresql:
+        $(MAKE) -C postgresql MAKELEVEL=0 all
+
+    Failure to do that can lead to strange error messages, typically about
+    missing header files.
+