tools/insn-fuzz: Provide IA32_DEBUGCTL consistently to the emulator

x86_emulates()'s is_branch_step() performs a speculative read of
IA32_DEBUGCTL, but doesn't squash exceptions should they arise.  In reality,
this MSR is always available.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

tools/fuzz/x86_instruction_emulator/fuzz-emul.c

@@ -402,7 +402,8 @@ enum {
     MSRI_STAR,
     MSRI_LSTAR,
     MSRI_CSTAR,
-    MSRI_SYSCALL_MASK
+    MSRI_SYSCALL_MASK,
+    MSRI_IA32_DEBUGCTLMSR,
 };
 
 static const unsigned int msr_index[MSR_INDEX_MAX] = {
@@ -413,7 +414,8 @@ static const unsigned int msr_index[MSR_INDEX_MAX] = {
     [MSRI_STAR]              = MSR_STAR,
     [MSRI_LSTAR]             = MSR_LSTAR,
     [MSRI_CSTAR]             = MSR_CSTAR,
-    [MSRI_SYSCALL_MASK]      = MSR_SYSCALL_MASK
+    [MSRI_SYSCALL_MASK]      = MSR_SYSCALL_MASK,
+    [MSRI_IA32_DEBUGCTLMSR]  = MSR_IA32_DEBUGCTLMSR,
 };
 
 static int fuzz_read_msr(