main: remove -no-debug flag

The -no-debug flag controls whether to emit DWARF debug information.
However, instead of limiting debug information altogether, I think it's
better to strip it off at the end if it isn't needed. For several
reasons:

  * Some parts of the compiler now rely on the presence of debug
    information for proper diagnostics.
  * It works better with the cache: there is no distinction between
    debug and no-debug builds.
  * It makes it easier (or possible at all) to enable debug information
    in the wasi-libc library without big downsides.

I'm doing this in a separate commit so this can be reverted if needed.

compileopts/config.go

@@ -209,9 +209,8 @@ func (c *Config) CFlags() []string {
 		cflags = append(cflags, "-nostdlibinc", "-Xclang", "-internal-isystem", "-Xclang", filepath.Join(root, "lib", "picolibc", "newlib", "libc", "include"))
 		cflags = append(cflags, "-I"+filepath.Join(root, "lib/picolibc-include"))
 	}
-	if c.EmitDWARF() {
-		cflags = append(cflags, "-g")
-	}
+	// Always emit debug information. It is optionally stripped at link time.
+	cflags = append(cflags, "-g")
 	return cflags
 }
 
@@ -250,12 +249,6 @@ func (c *Config) VerifyIR() bool {
 	return c.Options.VerifyIR
 }
 
-// EmitDWARF returns whether to add debug symbols to the IR, for debugging with
-// GDB and similar.
-func (c *Config) EmitDWARF() bool {
-	return c.Options.EmitDWARF
-}
-
 // Debug returns whether debug (DWARF) information should be retained by the
 // linker. The default varies by target but can be controlled with the -debug
 // command line flag.