Fix vs2010 project generation error when HEADER_FILE_ONLY is set.

In vs2010 a bad project file could be generated if a .c or .cxx file
was marked with HEADER_FILE_ONLY, if it was in a library that contained
both c and c++ code.  This fixes the error in the code, and adds a test
for this case.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -700,7 +700,7 @@ void cmVisualStudio10TargetGenerator::WriteCLSources()
         }
       (*this->BuildFileStream ) << sourceFile << "\"";
       // ouput any flags specific to this source file
-      if(cl && this->OutputSourceSpecificFlags(*source))
+      if(!header && cl && this->OutputSourceSpecificFlags(*source))
         {
         // if the source file has specific flags the tag
         // is ended on a new line

Tests/Complex/Executable/CMakeLists.txt

@@ -49,10 +49,17 @@ LINK_LIBRARIES(${COMPLEX_LIBS})
 SET_SOURCE_FILES_PROPERTIES(complex_nobuild.cxx PROPERTIES
   HEADER_FILE_ONLY 1)
 
+# Test forcing a .c file to not build.
+# This makes sure a mixed language library is created
+# with header file only sources
+SET_SOURCE_FILES_PROPERTIES(complex_nobuild.c PROPERTIES
+  HEADER_FILE_ONLY 1)
+
 ADD_EXECUTABLE(A A.cxx A.hh A.h A.txt)
 ADD_EXECUTABLE(complex complex testcflags.c )
 #  Sub1/NameConflictTest.c Sub2/NameConflictTest.c)
-ADD_EXECUTABLE(complex.file complex.file.cxx complex_nobuild.cxx)
+ADD_EXECUTABLE(complex.file complex.file.cxx complex_nobuild.cxx
+  complex_nobuild.c)
 IF(COMPLEX_TEST_CMAKELIB)
   TARGET_LINK_LIBRARIES(complex CMakeLib cmsys cmexpat cmzlib cmlibarchive cmbzip2 cmcurl)
 ENDIF(COMPLEX_TEST_CMAKELIB)

Tests/Complex/Executable/complex_nobuild.c

@@ -0,0 +1 @@
+#error "This file should not be compiled."