Write depfile for non-C-like tools

Bug: crbug/gn/89
Change-Id: I94071a3e9bb809684a6bd1f3e0416dcef17c7e1d
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/5261
Reviewed-by: Brett Wilson <brettw@google.com>
Commit-Queue: Julie Hockett <juliehockett@google.com>

tools/gn/ninja_toolchain_writer.cc

diff --git a/tools/gn/ninja_toolchain_writer.cc b/tools/gn/ninja_toolchain_writer.cc
index 6bfeb46..8956277 100644
--- a/tools/gn/ninja_toolchain_writer.cc
+++ b/tools/gn/ninja_toolchain_writer.cc
@@ -100,6 +100,9 @@
       // MSVC deps don't have a depfile.
       out_ << kIndent << "deps = msvc" << std::endl;
     }
+  } else if (!tool->depfile().empty()) {
+    WriteRulePattern("depfile", tool->depfile(), options);
+    out_ << kIndent << "deps = gcc" << std::endl;
   }
 
   // Use pool is specified.