third_party/marl: Add mips64 support to BUILD.gn

Bug: b/140546382
Change-Id: I2045aad2afc0918003117561dfe49aafbb4ef13a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/41048
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Ben Clayton <bclayton@google.com>

third_party/marl/BUILD.gn

diff --git a/third_party/marl/BUILD.gn b/third_party/marl/BUILD.gn
index c1fcb1b..6cdf092 100644
--- a/third_party/marl/BUILD.gn
+++ b/third_party/marl/BUILD.gn
@@ -59,9 +59,11 @@
       "src/osfiber_arm.c",
       "src/osfiber_asm_aarch64.S",
       "src/osfiber_asm_arm.S",
+      "src/osfiber_asm_mips64.S",
       "src/osfiber_asm_ppc64.S",
       "src/osfiber_asm_x64.S",
       "src/osfiber_asm_x86.S",
+      "src/osfiber_mips64.c",
       "src/osfiber_ppc64.c",
       "src/osfiber_x64.c",
       "src/osfiber_x86.c",