Move __system_properties_reload to LIBC from LIBC_PLATFORM

The zygote cannot have visiblity to LIBC_PLATFORM methods. Therefore,
move __system_properties_reload to LIBC, and rename it
__system_properties_zygote_reload, and indicate in comments that it
should not be used by non-zygote apps

Bug: 291814949
Test: atest CtsBionicRootTestCases
Change-Id: Iee8fa0c76b740543c05a433393f2f4bef36d6d3d
diff --git a/libc/bionic/system_property_api.cpp b/libc/bionic/system_property_api.cpp
index 847473a..8fdea59 100644
--- a/libc/bionic/system_property_api.cpp
+++ b/libc/bionic/system_property_api.cpp
@@ -29,6 +29,7 @@
 #define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
 #include <sys/_system_properties.h>
 
+#include <async_safe/CHECK.h>
 #include <system_properties/prop_area.h>
 #include <system_properties/system_properties.h>
 
@@ -131,6 +132,7 @@
 }
 
 __BIONIC_WEAK_FOR_NATIVE_BRIDGE
-int __system_properties_reload() {
+int __system_properties_zygote_reload(void) {
+  CHECK(getpid() == gettid());
   return system_properties.Reload(false) ? 0 : -1;
 }