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.

@@ -6584,10 +6584,16 @@
 @end smallexample
 
 The @option{-fstrict-aliasing} option is enabled at levels
 @option{-O2}, @option{-O3}, @option{-Os}.
 
+@item -fstrict-calling-conventions
+@opindex mstrict-calling-conventions
+Use strict ABI calling conventions even with local functions.
+This disable certain optimizations that may cause GCC to call local
+functions in a manner other than that described by the ABI.
+
 @item -fstrict-overflow
 @opindex fstrict-overflow
 Allow the compiler to assume strict signed overflow rules, depending
 on the language being compiled.  For C (and C++) this means that
 overflow when doing arithmetic with signed numbers is undefined, which