build: update Makefile comments for C++ version change (#10598)

Makefile

@@ -251,7 +251,7 @@ endif
 # Compile flags
 #
 
-# keep standard at C11 and C++11
+# keep standard at C11 and C++17
 MK_CPPFLAGS  = -Iggml/include -Iggml/src -Iinclude -Isrc -Icommon -DGGML_USE_CPU
 MK_CFLAGS    = -std=c11   -fPIC
 MK_CXXFLAGS  = -std=c++17 -fPIC