Fix link to documentation for -fdebug-prefix-map

BUG=None
TBR=dpranke
NOTRY=true

Change-Id: I1e8f248c467e553b580f7d1b5dcc17379f118504
Reviewed-on: https://chromium-review.googlesource.com/1093983Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565775}

build/config/compiler/BUILD.gn

@@ -95,7 +95,7 @@ declare_args() {
   # default only when goma is enabled on Linux because setting this to true may
   # make it harder to debug binaries.
   # See below reference for detail.
-  # https://chromium.googlesource.com/chromium/src/+/master/docs/linux_debugging.md#Source-level-debug-with-fdebug-prefix-map
+  # https://chromium.googlesource.com/chromium/src/+/master/docs/linux_debugging.md#Source-level-debug-with-fdebug_prefix_map
   strip_absolute_paths_from_debug_symbols = is_linux && use_goma
 
   # Allow projects that wish to stay on C++11 to override Chromium's default.