meson: Rename stdplus to stdplus_dep

This is the convention that meson builds should conform to.

Change-Id: Ia1a7e1a55e32200adbe37fa75ce02aee34df0219
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/meson.build b/src/meson.build
index dca95ce..b66fec2 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -72,7 +72,7 @@
   version: meson.project_version(),
   install: true)
 
-stdplus = declare_dependency(
+stdplus_dep = declare_dependency(
   dependencies: stdplus_deps,
   include_directories: stdplus_headers,
   link_with: stdplus_lib)