El problema se explica aquí:http ://www.randomactsofsentience.com/2013/05/gem-install-mysql2-missing-mysqlh-on-os.html . En resumen:
Cambie el archivo /usr/local/mysql/bin/mysql_config alrededor de la línea 120
cflags="-I$pkgincludedir -Wall -Wno-null-conversion -Wno-unused-private-field -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
cxxflags="-I$pkgincludedir -Wall -Wno-null-conversion -Wno-unused-private-field -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
a
cflags="-I$pkgincludedir -Wall -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
cxxflags="-I$pkgincludedir -Wall -Os -g -fno-strict-aliasing -DDBUG_OFF -arch x86_64 " #note: end space!
