Le problème est expliqué ici :http ://www.randomactsofsentience.com/2013/05/gem-install-mysql2-missing-mysqlh-on-os.html . En bref :
Modifiez le fichier /usr/local/mysql/bin/mysql_config vers la ligne 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!
à
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!
