configure: Reset X86ASM_DEP(FLAGS) when probing for the assembler program

These variables might be set from a previous probe run, but one or the
other program that is probed for may not grok the flags, resulting in
errors during assembling when the values of those variables are passed
to the assembler.

configure

@@ -4515,12 +4515,14 @@ EOF
             x86asmexe=$x86asmexe_probe
             x86asm_type=nasm
             x86asm_debug="-g -F dwarf"
+            X86ASMDEP=
             X86ASM_DEPFLAGS='-MD $(@:.o=.d)'
         elif check_cmd $x86asmexe_probe --version; then
             x86asmexe=$x86asmexe_probe
             x86asm_type=yasm
             x86asm_debug="-g dwarf2"
             X86ASMDEP='$(DEPX86ASM) $(X86ASMFLAGS) -M $(X86ASM_O) $< > $(@:.o=.d)'
+            X86ASM_DEPFLAGS=
         fi
         check_x86asm "movbe ecx, [5]" && enable x86asm
     }