Check vendor namespace for SPHAL namespace

Vendor APEX section should not separate SPHAL in generic, and also
default namespace does not contain vendor libs in the scope. This change
updates libvndksupport to check 'vendor' namespace when there is no
sphal namespace for vendor APEX section case.

Bug: 193861508
Test: AOSP CF x86_64 boot succeeded
Change-Id: I04cefc12be4c8ec261efb1688a8307b7061bf068

libvndksupport/linker.cpp

@@ -39,7 +39,7 @@ struct VendorNamespace {
 
 static VendorNamespace get_vendor_namespace() {
     static VendorNamespace result = ([] {
-        for (const char* name : {"sphal", "default"}) {
+        for (const char* name : {"sphal", "vendor", "default"}) {
             if (android_namespace_t* ns = android_get_exported_namespace(name)) {
                 return VendorNamespace{ns, name};
             }