Error building QMYSQL Plugin for Qt on Windows - qt

Question

I recently re-installed Qt - and now I am having issues with my MySQL drivers for Qt. I now get the error:
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QODBC QODBC3 QPSQL QPSQL7
So I am trying to build the QMYSQL Driver. So far I have...
Downloaded the MySQL Community installer by running mysql-installer-web-community-8.0.18.0.msi
And installed the x86 version of the MySQL Connector C 6.11, which saved to C:\Program Files (x86)\MySQL\MySQL Connector C 6.1
Opened a Developer Command Prompt for VS 2017 and ran:
CD "C:\Qt\5.12.6\Src\qtbase\src\plugins\sqldrivers"
qmake -- MYSQL_INCDIR="C:/Program Files (x86)/MySQL/MySQL Connector C 6.1/include" MYSQL_LIBDIR="C:/Program Files (x86)/MySQL/MySQL Connector C 6.1/lib"
Which seems to work, as I get "yes" for MySQL:
Running configuration tests...
Checking for DB2 (IBM)... no
Checking for InterBase... no
Checking for MySQL... yes
Checking for OCI (Oracle)... no
Checking for ODBC... yes
Checking for PostgreSQL... no
Checking for SQLite (version 2)... no
Checking for TDS (Sybase)... no
Done running configuration tests.
Configure summary:
Qt Sql Drivers:
DB2 (IBM) .............................. no
InterBase .............................. no
MySql .................................. yes
OCI (Oracle) ........................... no
ODBC ................................... yes
PostgreSQL ............................. no
SQLite2 ................................ no
SQLite ................................. yes
Using system provided SQLite ......... no
TDS (Sybase) ........................... no
Qt is now configured for building. Just run 'nmake'.
Once everything is built, you must run 'nmake install'.
Qt will be installed into 'C:\Qt\5.12.6\msvc2017_64'.
Prior to reconfiguration, make sure you remove any leftovers from
the previous build.
Note: I have also tried installing the x64 version of MySQL Connector C 6.1 instead of x86, but when I run QMAKE then (after adjusting the INCDIR and LIBDIR parameters from qmake) It says 'no' for MySQL - which I believe means that I am correct to be trying to use the x86 version.
Then from the same CMD I run: nmake sub-mysql but I get the error:
c:\qt\5.12.6\src\qtbase\src\plugins\sqldrivers\mysql\qsql_mysql_p.h(60): fatal error C1083: Cannot open include file: 'mysql.h': No such file or directory
main.cpp
c:\qt\5.12.6\src\qtbase\src\plugins\sqldrivers\mysql\qsql_mysql_p.h(60): fatal error C1083: Cannot open include file: 'mysql.h': No such file or directory
Generating Code...
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX86\x86\cl.EXE"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX86\x86\nmake.exe"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: 'cd' : return code '0x2'
Stop.
I've checked that 'mysql.h' DOES exist in 'C:\Program Files (x86)\MySQL\MySQL Connector C 6.1\include'.
Is there something else I am missing or doing wrong?
OS: Windows 10
Qt: 5.12.6
MySQL: C Connector 6.11 x86
Compiler: MSVC 2017