gen.py: Stop writing rule cc, GN has no C code.

Collapse cflags and cflags_cc into just cflags.
Also remove $defines from all the template files, nothing ever sets it.

Stop getting include_dirs and cflags off settings, it's never set.
'tool' is always 'cxx', so inline that and stop setting it on each binary.

No behavior change.

Bug: none
Change-Id: Ic01687acbd1e815151ec0308196339b3a2944e0c
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/6641
Commit-Queue: Brett Wilson <brettw@chromium.org>
Reviewed-by: Brett Wilson <brettw@chromium.org>
diff --git a/build/build_haiku.ninja.template b/build/build_haiku.ninja.template
index e59854b..ab117fb 100644
--- a/build/build_haiku.ninja.template
+++ b/build/build_haiku.ninja.template
@@ -1,11 +1,5 @@
-rule cc
-  command = $cc -MMD -MF $out.d $defines $includes $cflags $cflags_c -c $in -o $out
-  description = CC $out
-  depfile = $out.d
-  deps = gcc
-
 rule cxx
-  command = $cxx -MMD -MF $out.d $defines $includes $cflags $cflags_cc -c $in -o $out
+  command = $cxx -MMD -MF $out.d $includes $cflags -c $in -o $out
   description = CXX $out
   depfile = $out.d
   deps = gcc