[libc] skip test and return ENOSYS when processm_release unavailable

Author: SchrodingerZhu

libc/src/sys/mman/linux/process_mrelease.cpp

@@ -19,6 +19,7 @@
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, process_mrelease, (int pidfd, unsigned int flags)) {
+#ifdef SYS_process_mrelease
   long ret =
       LIBC_NAMESPACE::syscall_impl<int>(SYS_process_mrelease, pidfd, flags);
 
@@ -28,6 +29,13 @@ LLVM_LIBC_FUNCTION(int, process_mrelease, (int pidfd, unsigned int flags)) {
   }
 
   return 0;
+#else
+  // The system call is not available.
+  (void)pidfd;
+  (void)flags;
+  libc_errno = ENOSYS;
+  return -1;
+#endif
 }
 
 } // namespace LIBC_NAMESPACE_DECL

libc/test/src/sys/mman/linux/process_mrelease_test.cpp

@@ -18,7 +18,7 @@
 #include "test/UnitTest/LibcTest.h"
 
 #include <sys/syscall.h>
-
+#if defined(SYS_process_mrelease) && defined(SYS_pidfd_open)
 using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
 
 int pidfd_open(pid_t pid, unsigned int flags) {
@@ -72,3 +72,4 @@ TEST(LlvmLibcProcessMReleaseTest, ErrorNotKilled) {
 TEST(LlvmLibcProcessMReleaseTest, ErrorNonExistingPidfd) {
   EXPECT_THAT(LIBC_NAMESPACE::process_mrelease(-1, 0), Fails(EBADF));
 }
+#endif