engine.pl: ignore invalidcontinue.obj which is known to MSVC

Commit 4b623d8 (MSVC: link in invalidcontinue.obj for better
POSIX compatibility, 2014-03-29) introduced invalidcontinue.obj
into the Makefile output, which was not parsed correctly by the
buildsystem. Ignore it, as it is known to Visual Studio and,
there is no matching source file.

Only substitute filenames ending with .o when generating the
source .c filename, otherwise a .cbj file may be expected.

Split the .o and .obj processing; 'make' does not produce .obj
files.

In the future there may be source files that produce .obj files
so keep the two issues (.obj files with & without source files)
separate.

Signed-off-by: Philip Oakley <philipoakley@iee.org>

contrib/buildsystems/engine.pl

@@ -289,7 +289,7 @@ sub handleLibLine
 #    exit(1);
     foreach (@objfiles) {
         my $sourcefile = $_;
-        $sourcefile =~ s/\.o/.c/;
+        $sourcefile =~ s/\.o$/.c/;
         push(@sources, $sourcefile);
         push(@cflags, @{$compile_options{"${sourcefile}_CFLAGS"}});
         push(@defines, @{$compile_options{"${sourcefile}_DEFINES"}});
@@ -333,8 +333,12 @@ sub handleLinkLine
         } elsif ($part =~ /\.(a|lib)$/) {
             $part =~ s/\.a$/.lib/;
             push(@libs, $part);
-        } elsif ($part =~ /\.(o|obj)$/) {
+        } elsif ($part eq 'invalidcontinue.obj') {
+            # ignore - known to MSVC
+        } elsif ($part =~ /\.o$/) {
             push(@objfiles, $part);
+        } elsif ($part =~ /\.obj$/) {
+            # do nothing, 'make' should not be producing .obj, only .o files
         } else {
             die "Unhandled link option @ line $lineno: $part";
         }
@@ -343,7 +347,7 @@ sub handleLinkLine
 #    exit(1);
     foreach (@objfiles) {
         my $sourcefile = $_;
-        $sourcefile =~ s/\.o/.c/;
+        $sourcefile =~ s/\.o$/.c/;
         push(@sources, $sourcefile);
         push(@cflags, @{$compile_options{"${sourcefile}_CFLAGS"}});
         push(@defines, @{$compile_options{"${sourcefile}_DEFINES"}});