Add regression test for consecutive syscalls

unittests/FEXLinuxTests/tests/syscalls/consecutive_syscalls.cpp

@@ -0,0 +1,34 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include <sys/syscall.h>
+#include <unistd.h>
+
+// Regression test for issue #5942. Not ending the block after a syscall
+// can cause the register state to be incorrect afterwards, demonstrated here
+// by running two syscalls in a row in the same block.
+TEST_CASE("Two syscalls in one block") {
+  long Result {};
+#ifdef __x86_64__
+  __asm volatile(R"(
+    mov eax, %[GetPPid]
+    syscall
+    mov eax, %[GetPPid]
+    syscall
+  )"
+                 : "=a"(Result)
+                 : [GetPPid] "i"(SYS_getppid)
+                 : "rcx", "r11", "memory");
+#else
+  __asm volatile(R"(
+    mov eax, %[GetPPid]
+    int 0x80
+    mov eax, %[GetPPid]
+    int 0x80
+  )"
+                 : "=a"(Result)
+                 : [GetPPid] "i"(SYS_getppid)
+                 : "memory");
+#endif
+
+  CHECK(Result == ::getppid());
+}