riscv: add stage2_riscv to test matrix and bypass failing tests

test/behavior/usingnamespace.zig

@@ -11,6 +11,8 @@ const C = struct {
 };
 
 test "basic usingnamespace" {
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
+
     try std.testing.expect(C.B == bool);
 }
 
@@ -21,6 +23,8 @@ fn Foo(comptime T: type) type {
 }
 
 test "usingnamespace inside a generic struct" {
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
+
     const std2 = Foo(std);
     const testing2 = Foo(std.testing);
     try std2.testing.expect(true);
@@ -32,6 +36,8 @@ usingnamespace struct {
 };
 
 test "usingnamespace does not redeclare an imported variable" {
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
+
     try comptime std.testing.expect(@This().foo == 42);
 }
 
@@ -39,6 +45,7 @@ usingnamespace @import("usingnamespace/foo.zig");
 test "usingnamespace omits mixing in private functions" {
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
 
     try expect(@This().privateFunction());
     try expect(!@This().printText());
@@ -48,6 +55,8 @@ fn privateFunction() bool {
 }
 
 test {
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
+
     _ = @import("usingnamespace/import_segregation.zig");
 }
 
@@ -55,6 +64,7 @@ usingnamespace @import("usingnamespace/a.zig");
 test "two files usingnamespace import each other" {
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
 
     try expect(@This().ok());
 }
@@ -62,6 +72,7 @@ test "two files usingnamespace import each other" {
 test {
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
 
     const AA = struct {
         x: i32,
@@ -94,6 +105,8 @@ const Mixin = struct {
 };
 
 test "container member access usingnamespace decls" {
+    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
+
     var foo = Bar{};
     foo.two();
 }