Omit the "-c" argument from the preprocessing command

A command like "cc -c -E" is tautological; the -c is ignored, when
we explicitly specify that we want to preprocess only.

Since
llvm/llvm-project@6461e53
and llvm/llvm-project#98607, Clang now
warns about the unused "-c" argument in this case.

We already did omit the "-c" argument when preprocessing
(with cl.exe) for armasm, but do this for other cases as well.

Author: mstorsjo

gas-preprocessor.pl

@@ -155,6 +155,8 @@ ()
     $index++;
 }
 
+@preprocess_c_cmd = grep ! /^-c$/, @preprocess_c_cmd;
+
 my $tempfile;
 if ($as_type ne "armasm") {
     @gcc_cmd = map { /\.[csS]$/ ? qw(-x assembler -) : $_ } @gcc_cmd;
@@ -163,7 +165,6 @@ ()
     # Clang warns about unused -D parameters when invoked with "-x assembler".
     @gcc_cmd = grep ! /^-D/, @gcc_cmd;
 } else {
-    @preprocess_c_cmd = grep ! /^-c$/, @preprocess_c_cmd;
     @preprocess_c_cmd = grep ! /^-m/, @preprocess_c_cmd;
 
     @preprocess_c_cmd = grep ! /^-G/, @preprocess_c_cmd;