CONFIG: update c++ standard, some compiler rules (partially addresses #2209)

- migrate to c++14 for most compilers *except* gcc.
  There are still many systems in use with gcc-4.8.5, which does not
  support c++14.

- initial rules for nvidia compilers (pgi is will soon be defunct).
  Not fully tested...

CONFIG: provide fallback value for the user directory name

- in containers may have an unset USER env variable.
  Default to 'user' to prevent ugly looking directory names.

wmake/rules/General/Icc/c++

@@ -1,6 +1,9 @@
+#------------------------------------------------------------------------------
+# Intel compiler is new enough to support c++14
+#------------------------------------------------------------------------------
 SUFFIXES += .C .cc .cpp .cxx
 
-CC          = icpc -std=c++11
+CC          = icpc -std=c++14
 
 c++ARCH     =
 c++DBUG     =