build: adjust max_rss on a per-CI-host basis

This avoids pessimizing concurrency on all machines due to e.g. the macOS
machine having high memory usage across the board due to 16K page size.

This also adds max_rss to test-unit and test-c-abi since those tend to eat a
decent chunk of memory too.

test/tests.zig

@@ -2344,8 +2344,11 @@ fn addOneModuleTest(
     const libc_suffix = if (test_target.link_libc == true) "-libc" else "";
     const model_txt = target.cpu.model.name;
 
-    // wasm32-wasi builds need more RAM, idk why
-    const max_rss = if (target.os.tag == .wasi)
+    // These emulated targets need a lot more RAM for unknown reasons.
+    const max_rss = if (mem.eql(u8, options.name, "std") and
+        (target.cpu.arch == .hexagon or
+            (target.cpu.arch.isRISCV() and !resolved_target.query.isNative()) or
+            target.cpu.arch.isWasm()))
         options.max_rss * 2
     else
         options.max_rss;
@@ -2532,6 +2535,7 @@ const CAbiTestOptions = struct {
     skip_linux: bool,
     skip_llvm: bool,
     skip_release: bool,
+    max_rss: usize = 0,
 };
 
 pub fn addCAbiTests(b: *std.Build, options: CAbiTestOptions) *Step {
@@ -2604,6 +2608,7 @@ pub fn addCAbiTests(b: *std.Build, options: CAbiTestOptions) *Step {
                 .root_module = test_mod,
                 .use_llvm = c_abi_target.use_llvm,
                 .use_lld = c_abi_target.use_lld,
+                .max_rss = options.max_rss,
             });
 
             // This test is intentionally trying to check if the external ABI is