i386: Restore SMP functionality

When the switch to waf occurred, the SMP support in i386 was left out
causing it to accumulate a minor amount of cruft. This enables SMP for
the i386 BSPs that support it and updates them for the API drift that
has occurred since the change.

cpukit/score/cpu/i386/cpu_asm.S

@@ -67,11 +67,13 @@
 
         .p2align  1
         PUBLIC (_CPU_Context_switch)
+        PUBLIC (_CPU_Context_switch_no_return)
 
 .set RUNCONTEXT_ARG,   4                   /* save context argument */
 .set HEIRCONTEXT_ARG,  8                   /* restore context argument */
 
 SYM (_CPU_Context_switch):
+SYM (_CPU_Context_switch_no_return):
         movl      RUNCONTEXT_ARG(esp),eax  /* eax = running threads context */
         GET_SELF_CPU_CONTROL edx           /* edx has address for per_CPU information */
         movl      PER_CPU_ISR_DISPATCH_DISABLE(edx),ecx

cpukit/score/cpu/i386/include/rtems/score/cpu.h

@@ -572,6 +572,11 @@ void _CPU_Context_switch(
   Context_Control  *heir
 );
 
+RTEMS_NO_RETURN void _CPU_Context_switch_no_return(
+  Context_Control *executing,
+  Context_Control *heir
+);
+
 /*
  *  _CPU_Context_restore
  *

spec/build/cpukit/optsmp.yml

@@ -33,6 +33,10 @@ enabled-by:
 - arm/xilinx_zynq_picozed
 - arm/xilinx_zynq_pynq
 - arm/xilinx_zynq_microzed
+- i386/pc386
+- i386/pc486
+- i386/pc586
+- i386/pc686
 - powerpc/qoriq_e500
 - powerpc/qoriq_e6500_32
 - powerpc/qoriq_e6500_64