Add support for ARM builds by explicitly copying ARM header file

Fixes #72

Makefile

@@ -62,6 +62,7 @@ extract_source: $(PGDIR)
 	mkdir ./src/postgres/include
 	ruby ./scripts/extract_source.rb $(PGDIR)/ ./src/postgres/
 	cp $(PGDIR)/src/include/storage/dsm_impl.h ./src/postgres/include/storage
+	cp $(PGDIR)/src/include/port/atomics/arch-arm.h ./src/postgres/include/port/atomics
 	touch ./src/postgres/guc-file.c
 	# This causes compatibility problems on some Linux distros, with "xlocale.h" not being available
 	echo "#undef HAVE_LOCALE_T" >> ./src/postgres/include/pg_config.h

src/postgres/include/port/atomics/arch-arm.h

@@ -0,0 +1,26 @@
+/*-------------------------------------------------------------------------
+ *
+ * arch-arm.h
+ *	  Atomic operations considerations specific to ARM
+ *
+ * Portions Copyright (c) 2013-2017, PostgreSQL Global Development Group
+ *
+ * NOTES:
+ *
+ * src/include/port/atomics/arch-arm.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/* intentionally no include guards, should only be included by atomics.h */
+#ifndef INSIDE_ATOMICS_H
+#error "should be included via atomics.h"
+#endif
+
+/*
+ * 64 bit atomics on ARM32 are implemented using kernel fallbacks and thus
+ * might be slow, so disable entirely. On ARM64 that problem doesn't exist.
+ */
+#if !defined(__aarch64__) && !defined(__aarch64)
+#define PG_DISABLE_64_BIT_ATOMICS
+#endif  /* __aarch64__ || __aarch64 */