While installing mysqlclient package from pip, you may get above error.
Package name could be like this in requirements.txt.
mysqlclient @ git+https://github.com/PyMySQL/mysqlclient-python.git@ca630c01fb39f252a4c91a525e440beea4ac4447
Solution :
sudo apt-get install libmysqlclient-dev
For recent versions of debian/ubuntu (as of 2018) it issudo apt install default-libmysqlclient-dev