Add pidfd_open syscall helpers

FEXHeaderUtils/CMakeLists.txt

@@ -59,3 +59,16 @@ if (compiles)
   add_definitions(-DHAS_SYSCALL_RENAMEAT2=1)
 endif ()
 
+check_cxx_source_compiles(
+	"
+	#include <stdio.h>
+	#include <syscall.h>
+	int main() {
+	return ::syscall(SYS_pidfd_open, ::getpid(), 0);
+	}"
+  compiles)
+if (compiles)
+  message(STATUS "Has pidfd_open helper")
+  add_definitions(-DHAS_SYSCALL_PIDFD_OPEN=1)
+endif ()
+

FEXHeaderUtils/FEXHeaderUtils/Syscalls.h

@@ -79,5 +79,12 @@ inline int32_t renameat2(int olddirfd, const char *oldpath, int newdirfd, const
 #endif
 }
 
+inline int32_t pidfd_open(pid_t pid, unsigned int flags) {
+#if defined(DHAS_SYSCALL_PIDFD_OPEN) && DHAS_SYSCALL_PIDFD_OPEN
+  return ::syscall(SYS_pidfd_open, pid_t pid, unsigned int flags);
+#else
+  return -1;
+#endif
+}
 
 }