configure: Change the rdtsc check to a linker check

A compile-only test could succeed with an implicit function declaration.
Also move the check to the x86 section; rdtsc is x86-only.

configure

@@ -2643,8 +2643,6 @@ check_cc <<EOF && enable inline_asm
 void foo(void) { __asm__ volatile ("" ::); }
 EOF
 
-check_code cc intrin.h "__rdtsc()" && enable rdtsc
-
 _restrict=
 for restrict_keyword in restrict __restrict__ __restrict; do
     check_cc <<EOF && _restrict=$restrict_keyword && break
@@ -2743,6 +2741,8 @@ elif enabled sparc; then
 
 elif enabled x86; then
 
+    check_code ld intrin.h "__rdtsc()" && enable rdtsc
+
     enable local_aligned_8 local_aligned_16
 
     # check whether EBP is available on x86