DOC: update BuildIssues

- can compile with icc 17.0.1
- note the min gcc versions needed to compile clang

BuildIssues.txt

@@ -8,8 +8,8 @@ Intel Compiler
 --------------
 
   Since OpenFOAM uses C++11, a fairly recent version is required.
-
-  The Intel compiler - icc (ICC) 17.0.0 20160721 - has a bug that
+  The Intel compiler - icc (ICC) 17.0.1 20161005 is ok, but the
+  initial release - icc (ICC) 17.0.0 20160721 - has a bug that
   will result in these types of error messages.
 
     MatrixSpaceI.H(492): error: no instance of overloaded function
@@ -17,9 +17,6 @@ Intel Compiler
     BRowStart, BColStart>::operator=" matches the specified type
 
 
-  There is a update patch for the icc compiler to address this bug.
-
-
 ---
 VTK
 ---
@@ -28,15 +25,14 @@ If using the runTimePostProcessing to create on-the-fly images, you
 can either simply just compile ParaView-5.0.1 and these libraries will
 be used.
 
-If you decide to use a separate VTK compilation (for example for
+If you elect to use a separate VTK compilation (for example for
 off-screen rendering), it is advisable to reuse the VTK libraries that
 are provided with ParaView-5.0.1, by making an appropriate symlink
-prior to using makeVTK. This doesn't just reduce diskspace, but works
+prior to using makeVTK. This doesn't just reduce disk-space, but works
 much better than using the VTK-7.1.0.tar file.
 
-Building runTimePostProcessing with the 'plain' VTK-7.1.0 libraries
-generally works, but yields odd error and unpleasant looking errors
-when exiting:
+Using runTimePostProcessing with the 'plain' VTK-7.1.0 libraries does
+generally work, but does not exit cleanly:
 
     symbol lookup error: .../linux64Gcc/VTK-7.1.0/lib/libvtkCommonExecutionModel-7.1.so.1:
     undefined symbol: _ZN33vtkFilteringInformationKeyManager13ClassFinalizeEv
@@ -44,4 +40,24 @@ when exiting:
     symbol lookup error: .../linux64Gcc/VTK-7.1.0/lib/libvtkCommonDataModel-7.1.so.1:
     undefined symbol: _ZN49vtkInformationQuadratureSchemeDefinitionVectorKeyD1Ev
 
+This error appears to be suppressed if VTK is compiled with a Debug build-type.
+
+
+-------------------------
+Building on older systems
+-------------------------
+
+If the system gcc is too old for building OpenFOAM, a third-party gcc or
+clang/llvm installation can be used. If building clang/llvm, note that
+there are also minimum gcc/g++ requirements there:
+
+   Min gcc/g++
+   ===========   ==========
+    4.4          llvm-3.4.2
+    4.7          llvm-3.5.2 - llvm-3.7.0
+
+
+If your system compiler is too old to build the minimum required gcc or
+clang/llvm, it is just simply too old.
+
 --