runtime: move startupRandomData back to runtime2.go

In libgo it's referenced from os_gccgo.go on all platforms.

Fixes go/98496

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/280999

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-6857530fb1662c05a3ce754df2bd9fa5acd3a35b
+fa161cb71880cf80ef53fb4bf35dba8ee01af648
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/os_linux.go

@@ -178,10 +178,6 @@ func sysargs(argc int32, argv **byte) {
 	sysauxv(buf[:])
 }
 
-// startupRandomData holds random bytes initialized at startup. These come from
-// the ELF AT_RANDOM auxiliary vector.
-var startupRandomData []byte
-
 func sysauxv(auxv []uintptr) int {
 	var i int
 	for ; auxv[i] != _AT_NULL; i += 2 {

libgo/go/runtime/runtime2.go

@@ -885,6 +885,10 @@ type forcegcstate struct {
 	idle uint32
 }
 
+// startupRandomData holds random bytes initialized at startup. These come from
+// the ELF AT_RANDOM auxiliary vector.
+var startupRandomData []byte
+
 // extendRandom extends the random numbers in r[:n] to the whole slice r.
 // Treats n<0 as n==0.
 func extendRandom(r []byte, n int) {