Fix VS2017 approvals on AppVeyor

Because of a change in VS toolset, missing option <UseFullPaths>
is no longer interpreted as "don't pass /FC to the compiler", but
rather as "pass /FC to the compiler". This is problematic, because
/FC not only changes how much of the path is reporter by the compiler
(e.g. in `__FILE__` macro), but it also lower cases the path.

This lower-casing of the path broke our approval tests for VS2017
about 5 months ago.

Using CMake 3.13 (not yet released) would also let us fix it, but
for now we use a vcxproj.user file that is merged with the main project
and explicitly disables `/FC`.

projects/CMakeLists.txt

@@ -1,5 +1,17 @@
 include(MiscFunctions)
 
+####
+# Temporary workaround for VS toolset changes in 2017
+# We need to disable <UseFullPaths> property, but CMake doesn't support it
+# until 3.13 (not yet released)
+####
+if (MSVC)
+configure_file(${CATCH_DIR}/misc/SelfTest.vcxproj.user
+               ${CMAKE_BINARY_DIR}/projects
+               COPYONLY)
+endif(MSVC) #Temporary workaround
+
+
 # define the sources of the self test
 # Please keep these ordered alphabetically
 set(TEST_SOURCES