Fixed module support but cannot test for now

- gcc11 ICE when compiling with modules enabled;
- build2 0.14.0 does not allow enabling msvc modules support;

So for now we cannot test this code.

fmt/buildfile

@@ -5,15 +5,8 @@ imp_libs = # Implementation dependencies.
 ./ : lib{fmt}
 
 lib{fmt}: include/hxx{**} hxx{version} $imp_libs $int_libs
-
-if($config.fmt.enable_modules)
-{
-  lib{fmt}: src/mxx{fmt} # `fmt` C++ module
-}
-else
-{
-  lib{fmt}: src/cxx{** -fmt}
-}
+lib{fmt}: src/mxx{fmt} : include = ($config.fmt.enable_modules == true)
+lib{fmt}: src/cxx{** -fmt} : include = ($config.fmt.enable_modules == false)
 
 # Include the generated version header into the distribution (so that we don't
 # pick up an installed one) and don't remove it when cleaning in src (so that
@@ -26,7 +19,6 @@ hxx{version} : in{version} $src_root/manifest
   install = include/fmt
 }
 
-
 # Build options.
 #
 cxx.poptions =+ "-I$src_base/include" "-I$out_root" "-I$src_root"

tests/basics/buildfile

@@ -1,9 +1,13 @@
 import libs = fmt%lib{fmt}
 
-./ : exe{driver} : {cxx}{driver} hxx{tests.inl} $libs testscript{**}
+
 
 if($config.fmt.enable_modules)
 {
     ./ : exe{driver-modules} : {cxx}{driver-modules} hxx{tests.inl} $libs testscript{**}
 }
+else
+{
+    ./ : exe{driver} : {cxx}{driver} hxx{tests.inl} $libs testscript{**}
+}
 

tests/basics/driver.cxx

@@ -2,7 +2,6 @@
 #include <chrono>
 #include <vector>
 
-#include <fmt/version.h>
 #include <fmt/printf.h>
 #include <fmt/core.h>
 #include <fmt/format.h>