sv.h: SvPVx now equivalent to SvPV, et.al

These macros suffixed with 'x' are guaranteed to evaluate their
arguments just once.  Prior to this commit, they used PL_Sv to
accomplish that.  But since 1ef9039 in 5.37, the macros they call
only evaluate their arguments once, so the PL_Sv is superfluous.

sv.h

@@ -2078,29 +2078,15 @@ END_EXTERN_C
 #define SvUVx(sv) SvUV(sv)
 #define SvNVx(sv) SvNV(sv)
 
-#if defined(PERL_USE_GCC_BRACE_GROUPS)
-
-#  define SvPVx(sv, len) ({SV *_sv = (sv); SvPV(_sv, len); })
-#  define SvPVx_const(sv, len) ({SV *_sv = (sv); SvPV_const(_sv, len); })
-#  define SvPVx_nolen(sv) ({SV *_sv = (sv); SvPV_nolen(_sv); })
-#  define SvPVx_nolen_const(sv) ({SV *_sv = (sv); SvPV_nolen_const(_sv); })
-#  define SvPVutf8x(sv, len) ({SV *_sv = (sv); SvPVutf8(_sv, len); })
-#  define SvPVbytex(sv, len) ({SV *_sv = (sv); SvPVbyte(_sv, len); })
-#  define SvPVbytex_nolen(sv) ({SV *_sv = (sv); SvPVbyte_nolen(_sv); })
-
-#else /* __GNUC__ */
-
-/* These inlined macros use globals, which will require a thread
- * declaration in user code, so we avoid them under threads */
-
-#  define SvPVx(sv, len) ((PL_Sv = (sv)), SvPV(PL_Sv, len))
-#  define SvPVx_const(sv, len) ((PL_Sv = (sv)), SvPV_const(PL_Sv, len))
-#  define SvPVx_nolen(sv) ((PL_Sv = (sv)), SvPV_nolen(PL_Sv))
-#  define SvPVx_nolen_const(sv) ((PL_Sv = (sv)), SvPV_nolen_const(PL_Sv))
-#  define SvPVutf8x(sv, len) ((PL_Sv = (sv)), SvPVutf8(PL_Sv, len))
-#  define SvPVbytex(sv, len) ((PL_Sv = (sv)), SvPVbyte(PL_Sv, len))
-#  define SvPVbytex_nolen(sv) ((PL_Sv = (sv)), SvPVbyte_nolen(PL_Sv))
-#endif /* __GNU__ */
+/* The macros these now expand to no longer evaluate their arguments multiple
+ * times */
+#define SvPVx(sv, len)          SvPV(sv, len)
+#define SvPVx_const(sv, len)    SvPV_const(sv, len)
+#define SvPVx_nolen(sv)         SvPV_nolen(sv)
+#define SvPVx_nolen_const(sv)   SvPV_nolen_const(sv)
+#define SvPVutf8x(sv, len)      SvPVutf8(sv, len)
+#define SvPVbytex(sv, len)      SvPVbyte(sv, len)
+#define SvPVbytex_nolen(sv)     SvPVbyte_nolen(sv)
 
 #define SvIsCOW(sv)              (SvFLAGS(sv) & SVf_IsCOW)
 #define SvIsCOW_on(sv)           (SvFLAGS(sv) |= SVf_IsCOW)