Fix building with standalone sqlite3 >= 3.30.0

SQLite 3.30.0 changed the definition of SQLITE_DETERMINISTIC:
`-#define SQLITE_DETERMINISTIC    0x800`
`+#define SQLITE_DETERMINISTIC    0x000000800`

Meaning that the (older) system sqlite3 library and the pod have
different definitions, even though they're the same value.

We've been importing the system sqlite3 module in SQLiteObjc.h
even when linking against standalone sqlite.

I added a check to SQLiteObjc.h to import the sqlite3 pod when
we're using it, instead of always importing the system module.

This leads to there being only one definition in scope.

Author: bmwalters

SQLite.swift.podspec

@@ -50,7 +50,8 @@ Pod::Spec.new do |s|
     ss.private_header_files = 'Sources/SQLiteObjc/*.h'
 
     ss.xcconfig = {
-      'OTHER_SWIFT_FLAGS' => '$(inherited) -DSQLITE_SWIFT_STANDALONE'
+      'OTHER_SWIFT_FLAGS' => '$(inherited) -DSQLITE_SWIFT_STANDALONE',
+      'GCC_PREPROCESSOR_DEFINITIONS' => '$(inherited) SQLITE_SWIFT_STANDALONE=1'
     }
     ss.dependency 'sqlite3'
 

Sources/SQLiteObjc/include/SQLiteObjc.h

@@ -23,7 +23,11 @@
 //
 
 @import Foundation;
+#if defined(SQLITE_SWIFT_STANDALONE)
+@import sqlite3;
+#else
 @import SQLite3;
+#endif
 
 NS_ASSUME_NONNULL_BEGIN
 typedef NSString * _Nullable (^_SQLiteTokenizerNextCallback)(const char *input, int *inputOffset, int *inputLength);