str/cexpr: Add a function to make a constexpr generated string

This allows the user to generate an arbitrary length string at compile
time and convert it automatically to an std::array that is embedded in
the program for zero overhead runtime strings.

Change-Id: Ib6c2dd20cac53bb55e7a32e2fca194bdf0e06211
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/include/meson.build b/include/meson.build
index dc4de82..c3bfdfe 100644
--- a/include/meson.build
+++ b/include/meson.build
@@ -10,6 +10,7 @@
   'stdplus/raw.hpp',
   'stdplus/signal.hpp',
   'stdplus/str/cat.hpp',
+  'stdplus/str/cexpr.hpp',
   'stdplus/util/cexec.hpp',
   'stdplus/util/string.hpp',
   'stdplus/zstring.hpp',