test: Add mips64(el)-linux-(none,musl,gnuabi64) targets.

These take 3-4 minutes to run on my machine, i.e. they're not affected by the
LLVM compilation speed bug that affects mips32.

Author: alexrp

test/tests.zig

@@ -365,6 +365,54 @@ const test_targets = blk: {
             .slow_backend = true,
         },
 
+        .{
+            .target = .{
+                .cpu_arch = .mips64,
+                .os_tag = .linux,
+                .abi = .none,
+            },
+        },
+        .{
+            .target = .{
+                .cpu_arch = .mips64,
+                .os_tag = .linux,
+                .abi = .musl,
+            },
+            .link_libc = true,
+        },
+        .{
+            .target = .{
+                .cpu_arch = .mips64,
+                .os_tag = .linux,
+                .abi = .gnuabi64,
+            },
+            .link_libc = true,
+        },
+
+        .{
+            .target = .{
+                .cpu_arch = .mips64el,
+                .os_tag = .linux,
+                .abi = .none,
+            },
+        },
+        .{
+            .target = .{
+                .cpu_arch = .mips64el,
+                .os_tag = .linux,
+                .abi = .musl,
+            },
+            .link_libc = true,
+        },
+        .{
+            .target = .{
+                .cpu_arch = .mips64el,
+                .os_tag = .linux,
+                .abi = .gnuabi64,
+            },
+            .link_libc = true,
+        },
+
         .{
             .target = .{
                 .cpu_arch = .powerpc,