Add support for nasm assembler, patch by Peter Collingbourne (see #10069)

Alex

Modules/CMakeTestASM_NASMCompiler.cmake

@@ -0,0 +1,9 @@
+# This file is used by EnableLanguage in cmGlobalGenerator to
+# determine that the selected ASM_NASM "compiler" works.
+# For assembler this can only check whether the compiler has been found,
+# because otherwise there would have to be a separate assembler source file
+# for each assembler on every architecture.
+
+SET(ASM_DIALECT "_NASM")
+INCLUDE(CMakeTestASMCompiler)
+SET(ASM_DIALECT)