Update fmt lib, add recast, wip on recast pathfinder interface (broken atm)

libs/format/support/cmake/cxx11.cmake

@@ -20,7 +20,14 @@ if (FMT_USE_CPP11)
     check_cxx_source_compiles("
       #include <unistd.h>
       int main() {}" FMT_CPP11_UNISTD_H)
-    if (FMT_CPP11_CMATH AND FMT_CPP11_UNISTD_H)
+    # Check if snprintf works with -std=c++11. It may not in MinGW.
+    check_cxx_source_compiles("
+      #include <stdio.h>
+      int main() {
+        char buffer[10];
+        snprintf(buffer, 10, \"foo\");
+      }" FMT_CPP11_SNPRINTF)
+    if (FMT_CPP11_CMATH AND FMT_CPP11_UNISTD_H AND FMT_CPP11_SNPRINTF)
       set(CPP11_FLAG -std=c++11)
     else ()
       check_cxx_compiler_flag(-std=gnu++11 HAVE_STD_GNUPP11_FLAG)
@@ -37,6 +44,11 @@ if (FMT_USE_CPP11)
   endif ()
 endif ()
 
+if (CMAKE_CXX_STANDARD)
+  # Don't use -std compiler flag if CMAKE_CXX_STANDARD is specified.
+  set(CPP11_FLAG )
+endif ()
+
 set(CMAKE_REQUIRED_FLAGS ${CPP11_FLAG})
 
 # Check if variadic templates are working and not affected by GCC bug 39653: