Implement -fstrict-calling-conventions
Stock GCC is overly willing to violate the ABI when calling local functions,
such that it passes arguments in registers on i386.  This hampers debugging
with anything other than a fully-aware DWARF debugger, and is generally not
something we desire.
Implement a flag which disables this behaviour, enabled by default.  The flag is
global, though only effective on i386, to more easily allow its globalization
later which, given the odds, is likely to be necessary.

*** 4401,4410 ****
--- 4401,4411 ----
  
    /* Use register calling convention for local functions when possible.  */
    if (decl
        && TREE_CODE (decl) == FUNCTION_DECL
        && optimize
+       && (TARGET_64BIT || !flag_strict_calling_conventions)
        && !profile_flag)
      {
        /* FIXME: remove this CONST_CAST when cgraph.[ch] is constified.  */
        struct cgraph_local_info *i = cgraph_local_info (CONST_CAST_TREE(decl));
        if (i && i->local)
*** 4485,4495 ****
        return 2;
      }
  
    /* For local functions, pass up to SSE_REGPARM_MAX SFmode
       (and DFmode for SSE2) arguments in SSE registers.  */
!   if (decl && TARGET_SSE_MATH && optimize && !profile_flag)
      {
        /* FIXME: remove this CONST_CAST when cgraph.[ch] is constified.  */
        struct cgraph_local_info *i = cgraph_local_info (CONST_CAST_TREE(decl));
        if (i && i->local)
          return TARGET_SSE2 ? 2 : 1;
--- 4486,4497 ----
        return 2;
      }
  
    /* For local functions, pass up to SSE_REGPARM_MAX SFmode
       (and DFmode for SSE2) arguments in SSE registers.  */
!   if (decl && TARGET_SSE_MATH && optimize && !profile_flag &&
!     (TARGET_64BIT || !flag_strict_calling_conventions))
      {
        /* FIXME: remove this CONST_CAST when cgraph.[ch] is constified.  */
        struct cgraph_local_info *i = cgraph_local_info (CONST_CAST_TREE(decl));
        if (i && i->local)
          return TARGET_SSE2 ? 2 : 1;