Update openfoam (#11866)

* OpenFOAM: rationalize architecture options

- older versions of OpenFOAM had WM_ARCH_OPTION to choose a 32-bit
  build on 64-bit architectures. This is not exactly relevant anymore
  and has now been largely removed from OpenFOAM.

- simultaneously the newest version of OpenFOAM has rationalized the
  handling of special settings for KNL by rolling these into the
  compiler options. We now do the same thing here in spack.

  1. Reuse the internal variable arch_option to convey processor-specific
     optimizations and add these into the C++OPT=... statement.
  2. Drop spack support for configuring a 32-bit build on 64-bit
     hardware.

These changes can also be applied to older OpenFOAM versions, and to
various OpenFOAM forks without issue.

* update openfoam versions. New release 1906, patched 1812 version.

var/spack/repos/builtin/packages/openfoam-com/package.py

@@ -264,6 +264,8 @@ class OpenfoamCom(Package):
     list_depth = 2
 
     version('develop', branch='develop', submodules='True')  # Needs credentials
+    version('1906', 'ab7017e262c0c0fceec55c31e2153180')
+    version('1812_190531', 'a4b416838a8a76fdec22706a33c96de3')
     version('1812', '6a315687b3601eeece7ff7c7aed3d9a5')
     version('1806', 'bb244a3bde7048a03edfccffc46c763f')
     version('1712', '6ad92df051f4d52c7d0ec34f4b8eb3bc')
@@ -762,7 +764,7 @@ class OpenfoamArch(object):
     def __init__(self, spec, **kwargs):
         # Some user settings, to be adjusted manually or via variants
         self.compiler         = None   # <- %compiler
-        self.arch_option      = '64'   # (32/64-bit on x86_64)
+        self.arch_option      = ''     # Eg, -march=knl
         self.label_size       = None   # <- +int64
         self.precision_option = 'DP'   # <- +float32
         self.compile_option   = kwargs.get('compile-option', 'RpathOpt')
@@ -780,6 +782,10 @@ def __init__(self, spec, **kwargs):
         if '+float32' in spec:
             self.precision_option = 'SP'
 
+        # Processor/architecture-specific optimizations
+        if '+knl' in spec:
+            self.arch_option = '-march=knl'
+
         # spec.architecture.platform is like `uname -s`, but lower-case
         platform = spec.architecture.platform
 
@@ -787,13 +793,10 @@ def __init__(self, spec, **kwargs):
         target   = spec.architecture.target
 
         if platform == 'linux':
-            if target == 'i686':
-                self.arch_option = '32'  # Force consistency
-            elif target == 'x86_64':
-                if self.arch_option == '64':
-                    platform += '64'
+            if target == 'x86_64':
+                platform += '64'
             elif target == 'ia64':
-                platform += 'ia64'
+                platform += 'IA64'
             elif target == 'armv7l':
                 platform += 'ARM7'
             elif target == 'aarch64':
@@ -804,9 +807,7 @@ def __init__(self, spec, **kwargs):
                 platform += 'PPC64le'
         elif platform == 'darwin':
             if target == 'x86_64':
-                platform += 'Intel'
-                if self.arch_option == '64':
-                    platform += '64'
+                platform += '64'
         # ... and others?
 
         self.arch = platform
@@ -821,8 +822,6 @@ def __init__(self, spec, **kwargs):
             comp = self.compiler_mapping[comp]
         comp = comp.capitalize()
 
-        if '+knl' in spec:
-            comp += 'KNL'
         self.compiler = comp
         self.rule = self.arch + self.compiler
 
@@ -849,7 +848,6 @@ def foam_dict(self):
         """Returns a dictionary for OpenFOAM prefs, bashrc, cshrc."""
         return dict([
             ('WM_COMPILER',    self.compiler),
-            ('WM_ARCH_OPTION', self.arch_option),
             ('WM_LABEL_SIZE',  self.label_size),
             ('WM_PRECISION_OPTION', self.precision_option),
             ('WM_COMPILE_OPTION', self.compile_option),
@@ -918,6 +916,10 @@ def create_rules(self, projdir, foam_pkg):
                             if re.match(r'^\S+DBUG\s*=', line):
                                 outfile.write(' ')
                                 outfile.write(rpath)
+                            elif re.match(r'^\S+OPT\s*=', line):
+                                if self.arch_option:
+                                    outfile.write(' ')
+                                    outfile.write(self.arch_option)
                             outfile.write('\n')
 
             # MPI rules