Disable prctl test when building for arm or riscv. (#143627)

I'm setting up a buildbot for arm32 using qemu and qemu doesn't support
PR_GET_THP_DISABLE.
Disable the test for now while we figure out what to do about that.

Also disable for riscv because we may do the same for riscv buildbots.

libc/test/src/sys/prctl/linux/CMakeLists.txt

@@ -1,5 +1,10 @@
 add_custom_target(libc_sys_prctl_unittests)
 
+# Temporarily disable this test while setting up arm and riscv buildbots
+# using qemu, since PR_GET_THP_DISABLE is not supported on qemu.
+if (NOT (LIBC_TARGET_ARCHITECTURE_IS_ARM OR
+	 LIBC_TARGET_ARCHITECTURE_IS_RISCV32 OR
+	 LIBC_TARGET_ARCHITECTURE_IS_RISCV64))
 add_libc_unittest(
   prctl_test
   SUITE
@@ -13,3 +18,4 @@ add_libc_unittest(
     libc.test.UnitTest.ErrnoCheckingTest
     libc.test.UnitTest.ErrnoSetterMatcher
 )
+endif()

libc/test/src/sys/prctl/linux/prctl_test.cpp

@@ -34,6 +34,7 @@ TEST_F(LlvmLibcSysPrctlTest, GetSetName) {
 TEST_F(LlvmLibcSysPrctlTest, GetTHPDisable) {
   // Manually check errno since the return value logic here is not
   // covered in ErrnoSetterMatcher.
+  // Note that PR_GET_THP_DISABLE is not supported by QEMU.
   int ret = LIBC_NAMESPACE::prctl(PR_GET_THP_DISABLE, 0, 0, 0, 0);
   ASSERT_ERRNO_SUCCESS();
   // PR_GET_THP_DISABLE return (as the function result) the current