Remove extern "C" from fake declarations.

Assuming your C interfaces are appropriately wrapped for C++, it is
unnecessary to force the fakes to be declared extern "C", and doing so
causes any functions declared with C++ linkage to be impossible to fake
due to the conflicting linkage declarations.

examples/driver_testing/driver.test.fff.cpp

@@ -1,6 +1,7 @@
 extern "C"{
     #include "driver.h"
     #include "registers.h"
+    #include "hardware_abstraction.h"
 }
 #include "../../fff.h"
 #include <gtest/gtest.h>

fakegen.rb

@@ -271,23 +271,19 @@ def output_macro(arg_count, has_varargs, is_value_function)
   puts
   output_macro_header(declare_macro_name, saved_arg_count, has_varargs, return_type)
   indent {
-    extern_c {  # define argument capture variables
-      output_variables(saved_arg_count, has_varargs, is_value_function)
-    }
+    output_variables(saved_arg_count, has_varargs, is_value_function)
   }
 
   puts
   output_macro_header(define_macro_name, saved_arg_count, has_varargs, return_type)
   indent {
-    extern_c {
-      putd_backslash "FUNCNAME##_Fake FUNCNAME##_fake;"
-      putd_backslash function_signature(saved_arg_count, has_varargs, is_value_function) + "{"
-      indent {
-        output_function_body(saved_arg_count, has_varargs, is_value_function)
-      }
-      putd_backslash "}"
-      putd_backslash "DEFINE_RESET_FUNCTION(FUNCNAME)"
+    putd_backslash "FUNCNAME##_Fake FUNCNAME##_fake;"
+    putd_backslash function_signature(saved_arg_count, has_varargs, is_value_function) + "{"
+    indent {
+      output_function_body(saved_arg_count, has_varargs, is_value_function)
     }
+    putd_backslash "}"
+    putd_backslash "DEFINE_RESET_FUNCTION(FUNCNAME)"
   }
 
   puts
@@ -453,9 +449,9 @@ def define_fff_globals
   }
   putd "} fff_globals_t;"
   puts
-  putd_backslash "FFF_EXTERN_C"
+  putd "FFF_EXTERN_C"
   putd "extern fff_globals_t fff;"
-  putd_backslash "FFF_END_EXTERN_C"
+  putd "FFF_END_EXTERN_C"
   puts
   putd_backslash "#define DEFINE_FFF_GLOBALS"
   indent {
@@ -477,14 +473,6 @@ def define_fff_globals
   }
 end
 
-def extern_c
-  putd_backslash "FFF_EXTERN_C"
-  indent { 
-    yield
-  }
-  putd_backslash "FFF_END_EXTERN_C"
-end
-
 def in_struct
   putd_backslash "typedef struct FUNCNAME##_Fake {"
   indent {