Work around Intel compiler oddities

For some reason, and only in certain cases, the built-in
preprocessor of ifort cannot handle constructs such as

  #define FOO bar

  print *, "foo&
  &FOO&
  &baz"

or more specifically

  #define DATATYPE double

  print *, some_&
  &DATATYPE&
  &_routine

which, however, are quite handy. GCC seems to handle those as
expected.

configure.ac

@@ -113,6 +113,7 @@ if test x"$with_mpi" = x"yes"; then
     AC_MSG_ERROR([Could not compile an MPI Fortran program])
   fi
 fi
+
 if test x"${enable_openmp}" = x"yes"; then
   AX_ELPA_OPENMP
   if test "$ac_cv_prog_fc_openmp" = unsupported; then
@@ -1099,6 +1100,20 @@ AC_CONFIG_FILES([
   ${PKG_CONFIG_FILE}:elpa.pc.in
 ])
 
+AC_MSG_CHECKING([if workaround for Intel's broken preprocessor is needed])
+if test x"$FC" = x"mpiifort" ; then
+	need_manual_cpp=yes
+fi
+if test x"$FC" = x"ifort" ; then
+	need_manual_cpp=yes
+fi
+if test x"$need_manual_cpp" = x"yes" ; then
+	AC_MSG_RESULT([yes])
+	FC="\$(top_srcdir)/manual_cpp $FC"
+else
+	AC_MSG_RESULT([no])
+fi
+
 AC_OUTPUT
 
 if test "${can_compile_avx}" = "no" ; then

manual_cpp

+#!/usr/bin/python
+from __future__ import print_function
+import os
+import sys
+import subprocess
+
+def cpp_arg(arg):
+    return arg.startswith("-I") or \
+           arg.startswith("-D") or \
+           arg.startswith("-U")
+
+
+def check_call(args, **kwargs):
+    if os.getenv("V") == "1":
+        print(" ".join(args))
+    return subprocess.check_call(args, **kwargs)
+
+def check_call_redirect(args, filename=None, **kwargs):
+    if os.getenv("V") == "1":
+        print(" ".join(args), ">", filename)
+    with open(filename, "wb") as fd:
+        return subprocess.check_call(args, stdout=fd, **kwargs)
+
+
+args = sys.argv[1:]
+cpp_args = filter(cpp_arg, args)
+
+files = filter(lambda q : q.endswith(".F90"), args)
+args = filter(lambda q : not q.endswith(".F90"), args)
+if len(files) > 1:
+    raise Exception("Specify exactly one .F90 file")
+elif len(files) == 0:
+    # No .F90 file specified, execute program as-is
+    os.execvp(args[0], args[1:])
+
+tmp_filename = "manually_preprocessed_" + file.replace("/", "__")
+
+try:
+    output = args.index("-o")
+    outputname = args[output + 1]
+    tmp_filename += "-" + outputname.replace("/", "__") + ".F90"
+except ValueError:
+    pass
+
+# preprocess
+check_call_redirect(["cpp","-P", "-traditional", "-Wall", "-Werror"] + cpp_args + [file], filename=tmp_filename)
+
+# compile
+check_call(args + [tmp_filename])
+
+# cleanup
+os.remove(tmp_filename)