This patch fixes doc generation when using fpdoc-2.6.0. It should not be
applied if starting with a newer fpdoc. It is not required to build the
compiler, but causes fpdoc-2.6.0 to crach due to newly added syntax extension
which it does not support.
We are adding a patch to be applied just before using fpdoc and get reverted
just after and patching the docs make file to apply it at the right time.

diff --git a/fpcdocs/rtl/linux/oldlinux.pp b/fpcdocs/rtl/linux/oldlinux.pp
index d006856..dc92266 100644
--- a/fpcdocs/fix-doc-build-with-fpdoc-2.6.0.diff
+++ b/fpcdocs/fix-doc-build-with-fpdoc-2.6.0.diff
@@ -0,0 +1,13 @@
+diff --git a/fpcsrc/rtl/linux/oldlinux.pp b/fpcsrc/rtl/linux/oldlinux.pp
+index d006856..dc92266 100644
+--- ../fpcsrc/rtl/linux/oldlinux.pp
++++ ../fpcsrc/rtl/linux/oldlinux.pp
+@@ -12,7 +12,7 @@
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ 
+ **********************************************************************}
+-unit oldlinux deprecated 'Use Baseunix/Unix';
++unit oldlinux deprecated;
+ 
+ Interface
+ 
diff --git a/fpcdocs/Makefile.hev b/fpcdocs/Makefile.hev
index a357d14..e2c8d20 100644
--- a/fpcdocs/Makefile
+++ b/fpcdocs/Makefile
@@ -2427,7 +2427,9 @@ ipf:
 	$(MAKE) html HTMLFMT=ipf
 endif  # INSTALLDEBUG
 hevea:
+	patch -p0 -i fix-doc-build-with-fpdoc-2.6.0.diff
 	$(MAKE) html USEHEVEA=1
+	patch -p0 -R -i fix-doc-build-with-fpdoc-2.6.0.diff
 l2h:
 	$(MAKE) html USEL2H=1
 4ht: