Add --ftime-trace to dmd

changelog/dmd.ftime-trace.dd

@@ -0,0 +1,16 @@
+Build time profiling has been added to dmd
+
+The `-ftime-trace` switch that the LDC compiler already has, is now also available in dmd.
+It can be used to figure out which parts of your code take the longest to compile, so you can optimize your build times.
+
+$(CONSOLE
+dmd --ftime-trace app.d
+)
+
+This will output `app.o.time-trace`.
+
+A different output file can be selected with `--ftime-trace-file=trace.json`.
+
+The output is in Google Chrome's profiler format, which can be converted to readable text with the included `timetrace2txt` tool, or be viewed in an interactive viewer like [ui.perfetto.dev](https://ui.perfetto.dev).
+
+See also this YouTube tutorial: [Easily Reduce Build Times by Profiling the D Compiler](https://www.youtube.com/watch?v=b8wZqU5t9vs)

compiler/src/build.d

@@ -1587,7 +1587,7 @@ auto sourceFiles()
             stringtable.d utf.d
         "),
         common: fileArray(env["COMMON"], "
-            bitfields.d file.d int128.d blake3.d outbuffer.d smallbuffer.d charactertables.d identifiertables.d
+            bitfields.d file.d int128.d blake3.d outbuffer.d smallbuffer.d timetrace.d charactertables.d identifiertables.d
         "),
         commonHeaders: fileArray(env["COMMON"], "
             outbuffer.h

compiler/src/dmd/cli.d

@@ -375,6 +375,27 @@ dmd -cov -unittest myprog.d
             "generate position independent executables",
             cast(TargetOS) (TargetOS.all & ~(TargetOS.Windows | TargetOS.OSX))
         ),
+        Option("-ftime-trace",
+            "turn on compile time profiler, generate JSON file with results",
+            "Per function, the time to analyze it, call it from CTFE, generate code for it etc. will be measured,
+            and events with a time longer than 500 microseconds (adjustable with `-ftime-trace-granularity`)
+            will be recorded.
+            The profiling result is output in the Chrome Trace Event Format,
+            $(LINK2 https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview, described here).
+            This can be turned into a more readable text file with the included tool `timetrace2txt`, or inspected
+            with an interactive viewer such as $(LINK2 https://ui.perfetto.dev/, Perfetto)."
+        ),
+        Option("-ftime-trace-granularity=",
+            "Minimum time granularity (in microseconds) traced by time profiler (default: 500)",
+            "Measured events shorter than the specified time will be discarded from the output.
+            Set it too high, and interesting events may not show up in the output.
+            Set too low, and the profiler overhead will be larger, and the output will be cluttered with tiny events."
+        ),
+        Option("-ftime-trace-file=<filename>",
+            "specify output file for --ftime-trace",
+            "By default, the output name is the same as the first object file name, but with the `.time-trace` extension appended.
+            A different filename can be chosen with this option, including a path relative to the current directory or an absolute path."
+        ),
         Option("g",
             "add symbolic debug info",
             `$(WINDOWS