S_new_SV: mark args unused, make inline, rename with Perl_ prefix

When sv_inline.h was created in
Perl@75acd14
and a number of things moved into it, the S_new_SV debugging function should
have been made PERL_STATIC_INLINE and given the Perl_ prefix. This commit
now does those things. It also marks the arguments to Perl_new_SV as
PERL_UNUSED_ARG, reducing warnings on some builds.

sv_inline.h

@@ -71,10 +71,13 @@ SV* Perl_more_sv(pTHX);
 
 #ifdef DEBUG_LEAKING_SCALARS
 /* provide a real function for a debugger to play with */
-STATIC SV*
-S_new_SV(pTHX_ const char *file, int line, const char *func)
+PERL_STATIC_INLINE SV*
+Perl_new_SV(pTHX_ const char *file, int line, const char *func)
 {
     SV* sv;
+    PERL_UNUSED_ARG(file);
+    PERL_UNUSED_ARG(line);
+    PERL_UNUSED_ARG(func);
 
     if (PL_sv_root)
         uproot_SV(sv);
@@ -102,7 +105,7 @@ S_new_SV(pTHX_ const char *file, int line, const char *func)
 
     return sv;
 }
-#  define new_SV(p) (p)=S_new_SV(aTHX_ __FILE__, __LINE__, FUNCTION__)
+#  define new_SV(p) (p)=Perl_new_SV(aTHX_ __FILE__, __LINE__, FUNCTION__)
 
 #else
 #  define new_SV(p) \