[MIPS] Enable tcmalloc for mipsel

With these two merged:
https://chromium-review.googlesource.com/c/chromium/src/+/904303
https://chromium-review.googlesource.com/c/chromium/src/+/909216
we can enable tcmalloc for mipsel.

Bug: 810356
Change-Id: Idd63cb9a0e1a9582047ad203edf160b0c532f854
Reviewed-on: https://chromium-review.googlesource.com/947948Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542685}

build/config/allocator.gni

@@ -5,9 +5,9 @@
 import("//build/config/sanitizers/sanitizers.gni")
 
 # Temporarily disable tcmalloc on arm64 linux to get rid of compilation errors.
-if (is_android || current_cpu == "mipsel" || is_mac || is_ios ||
-    is_asan || is_lsan || is_tsan || is_msan || is_win || is_syzyasan ||
-    is_fuchsia || (is_linux && target_cpu == "arm64")) {
+if (is_android || is_mac || is_ios || is_asan || is_lsan || is_tsan ||
+    is_msan || is_win || is_syzyasan || is_fuchsia ||
+    (is_linux && target_cpu == "arm64")) {
   _default_allocator = "none"
 } else {
   _default_allocator = "tcmalloc"