compiler: support //go:linknamestd pragma

Go 1.27 introduced the //go:linknamestd directive, a standard-library
variant of //go:linkname that does not require importing "unsafe". The
iter package switched to it for referencing runtime.newcoro and
runtime.coroswitch, which caused "linker could not find symbol
iter.newcoro / iter.coroswitch" errors when building with Go 1.27.

Handle //go:linknamestd the same as //go:linkname, bypassing the unsafe
import requirement, and add test coverage in the pragma compiler test.

Signed-off-by: deadprogram <ron@hybridgroup.com>

compiler/testdata/pragma.ll

@@ -33,6 +33,8 @@ entry:
 
 declare void @somepkg.someFunction2(ptr) #0
 
+declare void @somepkg.someFunctionStd(ptr) #0
+
 ; Function Attrs: inlinehint nounwind
 define hidden void @main.inlineFunc(ptr %context) unnamed_addr #3 {
 entry: