Use a separate preprocessor rule

Otherwise, we end up passing both -c and -E to the compiler.

pkg/libpng/gen.lua

@@ -14,9 +14,7 @@ build('awk', '$outdir/pnglibconf.tf4', {
 build('awk', '$outdir/pnglibconf.c', '$outdir/pnglibconf.tf4', {
 	expr='-f $srcdir/scripts/options.awk out=/dev/stdout',
 })
-build('cc', '$outdir/pnglibconf.tf1', {'$outdir/pnglibconf.c', '||', 'pkg/zlib/headers'}, {
-	cflags='$cflags -E -MT $outdir/pnglibconf.tf1',
-})
+build('cpp', '$outdir/pnglibconf.tf1', {'$outdir/pnglibconf.c', '||', 'pkg/zlib/headers'})
 build('awk', '$outdir/include/pnglibconf.h', '$outdir/pnglibconf.tf1', {
 	expr='-f $srcdir/scripts/dfn.awk out=/dev/stdout',
 })

pkg/strace/gen.lua

@@ -8,9 +8,7 @@ cflags{
 	'-I $outdir',
 }
 
-build('cc', '$outdir/ioctl_iocdef.i', '$srcdir/ioctl_iocdef.c', {
-	cflags='$cflags -P -E -MT $outdir/ioctl_iocdef.i',
-})
+build('cpp', '$outdir/ioctl_iocdef.i', '$srcdir/ioctl_iocdef.c')
 build('sed', '$outdir/ioctl_iocdef.h', '$outdir/ioctl_iocdef.i', {
 	expr=[[-n 's/^DEFINE HOST/#define /p']],
 })
@@ -41,8 +39,8 @@ end)
 
 local mpers = lines('mpers.txt')
 for _, f in ipairs(mpers) do
-	build('cc', '$outdir/'..f..'.mpers.i', '$srcdir/'..f, {
-		cflags='$cflags -P -E -MT $outdir/'..f..'.mpers.i -DIN_MPERS_BOOTSTRAP',
+	build('cpp', '$outdir/'..f..'.mpers.i', '$srcdir/'..f, {
+		cflags='$cflags -DIN_MPERS_BOOTSTRAP',
 	})
 end
 
@@ -56,9 +54,7 @@ makempers('printers.h', 'printers.awk')
 makempers('native_printer_decls.h', 'printerdecls.awk')
 makempers('native_printer_defs.h', 'printerdefs.awk')
 
-build('cc', '$outdir/syscallent.i', '$srcdir/linux/x86_64/syscallent.h', {
-	cflags='$cflags -P -E -MT $outdir/syscallent.i',
-})
+build('cpp', '$outdir/syscallent.i', '$srcdir/linux/x86_64/syscallent.h')
 build('awk', '$outdir/scno-syscallent.h', {'$outdir/syscallent.i', '|', '$dir/scno.awk'}, {
 	expr='-f $dir/scno.awk',
 })

rules.ninja

@@ -9,6 +9,12 @@ rule cc
   deps = gcc
   description = CC $out
 
+rule cpp
+  command = $cc -MMD -MF $out.d $cflags -E -P -o $out $in
+  depfile = $out.d
+  deps = gcc
+  description = CPP $out
+
 rule as
   command = $as $asflags -o $out $in