Add config.{c,cxx}.std

These values override {c,cxx}.std specified at the project level. In
particular, this allows us to force a specific standard for all the
projects in a build configuration, for example:

b create: conf/,cc config.cxx=g++ config.cxx.std=experimental

1 files changed, 3 insertions, 0 deletions

diff --git a/build2/variable.hxx b/build2/variable.hxx
index 5e6ad2f..01e7038 100644
--- a/build2/variable.hxx
+++ b/build2/variable.hxx
@@ -339,6 +339,9 @@ namespace build2
     template <typename T> value& operator= (T);
     template <typename T> value& operator+= (T);
 
+    template <typename T> value& operator= (T* v) {
+      return v != nullptr ? *this = *v : *this = nullptr;}
+
     template <typename T> value& operator+= (T* v) {
       return v != nullptr ? *this += *v : *this;}