[flang][driver] Make `flang` ignore `-Mfree/-Mfixed`

[awarzynski]

Summary

-Mfixed is not supported by the new driver and hence
flang, the bash wrapper script, forwards it to the host compiler.
The forwarded options are used by the host compiler when compiling the
unparsed files. As the unparsed source files are always in the free
form, forwarding -Mfixed is problematic.

With this patch, -Mfixed (and -Mfree for consistency) will be
ignored altogether. The user will only see a warning. This is not a
particularly sound approach, but flang is only a temporary solution
for us and this workaround is a fair compromise.

[Leporacanthicus]

LGTM

[sscalpone]

flang/tools/f18/flang.in

218

I don't think there's a need for a warning. The throwaway driver dropped these options too.

[awarzynski]

Remove the warning

[sscalpone]

Looks good! Thanks

flang/tools/f18/flang.in

if
       [[ $opt == "-fxor-operator" ]] ||
       [[ $opt == "-help" ]] ||
       [[ $opt == "-nocpp" ]] ||
       [[ $opt == "-pedantic" ]] ||
       [[ $opt =~ ^-std=.* ]] ||
       [[ $opt =~ ^-U.* ]] ||
       [[ $opt == "-Werror" ]]; then
       flang_opts+=($opt)
+    elif
+      # These options are not supported by `flang-new`. There is also no point
+      # in forwarding them to the host compiler as the output from
+      # `-fdebug-unparse` will always be in free form.
+      [[ $opt == "-Mfixed" ]] || [[ $opt == "-Mfree" ]]; then
+      :
     elif [[ $opt =~ -I.* ]] || [[ $opt =~ -J.* ]]; then
       # Options that are needed for both Flang and the external driver.
       flang_opts+=($opt)
       fc_opts+=($opt)
     else
       # All other options are claimed for the external driver.
       fc_opts+=($opt)
     fi