fix baremetal runtime: rename malloc and co. export names

src/runtime/baremetal.go

@@ -37,20 +37,20 @@ func growHeap() bool {
 	return false
 }
 
-//export malloc
+//export tinygo_malloc
 func libc_malloc(size uintptr) unsafe.Pointer {
 	// Note: this zeroes the returned buffer which is not necessary.
 	// The same goes for bytealg.MakeNoZero.
 	return alloc(size, nil)
 }
 
-//export calloc
+//export tinygo_calloc
 func libc_calloc(nmemb, size uintptr) unsafe.Pointer {
 	// No difference between calloc and malloc.
 	return libc_malloc(nmemb * size)
 }
 
-//export free
+//export tinygo_free
 func libc_free(ptr unsafe.Pointer) {
 	free(ptr)
 }