Build with the system NSPR library instead of the bundled version.

Originally based on this Debian patch:
https://salsa.debian.org/chromium-team/chromium/-/blob/master/debian/patches/system/nspr.patch

diff --git a/base/BUILD.gn b/base/BUILD.gn
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -159,6 +159,12 @@
   flags = [ "CRONET_BUILD=$is_cronet_build" ]
 }
 
+if (is_linux) {
+  ldflags = [
+    "-lnspr4",
+  ]
+}
+
 use_epoll = is_linux || is_chromeos || is_android
 
 # Base and everything it depends on should be a static library rather than
@@ -809,8 +815,6 @@
     "task/updateable_sequenced_task_runner.h",
     "test/scoped_logging_settings.h",
     "test/spin_wait.h",
-    "third_party/nspr/prtime.cc",
-    "third_party/nspr/prtime.h",
     "thread_annotations.h",
     "threading/hang_watcher.cc",
     "threading/hang_watcher.h",
diff --git a/base/time/pr_time_unittest.cc b/base/time/pr_time_unittest.cc
--- a/base/time/pr_time_unittest.cc
+++ b/base/time/pr_time_unittest.cc
@@ -6,7 +6,7 @@
 #include <time.h>
 
 #include "base/compiler_specific.h"
-#include "base/third_party/nspr/prtime.h"
+#include <nspr/prtime.h>
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
diff --git a/base/time/time.cc b/base/time/time.cc
--- a/base/time/time.cc
+++ b/base/time/time.cc
@@ -15,7 +15,7 @@
 #include "base/check.h"
 #include "base/format_macros.h"
 #include "base/strings/stringprintf.h"
-#include "base/third_party/nspr/prtime.h"
+#include <nspr/prtime.h>
 #include "base/time/time_override.h"
 #include "build/build_config.h"