Compiling FFmpeg with Libass using MSVC - c++

Question

First a bit of background.
I'm trying to compile ffmpeg on windows with the libass extensions/configuration option.
Using the visual studio project libass-msvc I built libass using Visual Studio as a static lib.
I then installed MinGW with MSYS and pkg-config. Following the instructions on the ffmpeg MSVC installation guide I configured the environment to build with the MSVC linker and to build in x64.
When I try to configure libass for compilation using ./configure --enable-libass --toolchain=msvc I get the following error in the log file:
File not found ass/ass.h
pkg-config can not find libass
I have tried the following to fix this.
Create a .pc file for libass and add this to the PKG_CONFIG_PATH environment variable. See file content below. (After doing this pkg-config libass --version prints 0.81, not the right version number but at least something.)
Copy libass .h files into a MinGW/include/ass folder and the .lib file into the MinGW/libs folder.
Add libass include and bin folders to PATH environment variable
Download libass and dependencies source then try to build it using MSYS with MSVC compiler. My aim here was to be able to use "make install" and let MinGW install libass to the correct locations. After hours of trying to fix linker errors, I abandoned this idea as some of the libass dependencies make files only work with the GCC GNU compiler.
Compile libass with GCC GNU using MinGW make/make install then try and install libass using the GNU libs. Again this led to linker errors (I know this was a bad idea but was worth a try).
Tried using extra lib and include build configuration options --extra-cflags="ffmpeg-dir/extra/include" \
--extra-ldflags="ffmped-dir/extra/ffmpeg_build/lib" then adding the libs and .h files into those locations
.pc file
libass.pc:
prefix=/MinGW
includedir=libass-directory/include
libdir=libass-director/x64/bin/
Name: libass
Description: Libass project
Version: 0.13.7
I am now completely stuck and out of ideas if anyone could give any insight or suggestions into what I'm doing wrong that would be fantastic.
Update
I created INCLUDE and LIBDIR environment path variable containing the libass paths. Which now correctly includes libass. However, I now get the following linker error for the function check_ass_library_init.
check_func_headers ass/ass.h ass_library_init
check_ld cc
check_cc
BEGIN ./ffconf.RZMYFWdc/test.c
1 #include
2 #include
3 long check_ass_library_init(void) { return (long)
ass_library_init; }
4 int main(void) { int ret = 0;
5 ret |= ((intptr_t)check_ass_library_init) & 0xFFFF;
6 return ret; }
END ./ffconf.RZMYFWdc/test.c
cl -D_ISOC99_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -
D_USE_MATH_DEFINES -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -
D_WIN32_WINNT=0x0502 -nologo -c -Fo./ffconf.RZMYFWdc/test.o
./ffconf.RZMYFWdc/test.c
test.c
./ffconf.RZMYFWdc/test.c(3): warning C4311: 'type cast': pointer truncation
from 'ASS_Library *(__cdecl *)(void)' to 'long'
./compat/windows/mslink -nologo -out:./ffconf.RZMYFWdc/test.exe
./ffconf.RZMYFWdc/test.o psapi.lib advapi32.lib shell32.lib ole32.lib
test.o : error LNK2019: unresolved external symbol ass_library_init
referenced in function check_ass_library_init
./ffconf.RZMYFWdc/test.exe : fatal error LNK1120: 1 unresolved externals
ERROR: libass not found using pkg-config
The libass test project which uses ass_library_init compiles fine using the same lib files, the libs appear to be fine.
From what I see from this line "./compat/windows/mslink -nologo -out:./ffconf.RZMYFWdc/test.exe ./ffconf.RZMYFWdc/test.o psapi.lib advapi32.lib shell32.lib ole32.lib" libass is not being passed to the linker.
I suspect that the configuration file is not creating the link to libass in the make file when compiling with MSVC.
Am I correct or am I going about compiling this in the wrong way?