w3m: Fix redefinition of struct file_handle for Linuxbrew
w3m: Fix redefinition of struct file_handle for Linuxbrew

Fix istream.h:23:8: error: redefinition of 'struct file_handle'
See https://sourceforge.net/p/w3m/patches/62/

See Homebrew/linuxbrew#159
Closes Homebrew/linuxbrew#708

ebouaziz/linuxbrew,Linuxbrew/linuxbrew,reelsense/linuxbrew,bukzor/linuxbrew,Homebrew/linuxbrew,saketkc/linuxbrew,DoomHammer/linuxbrew,SuperNEMO-DBD/cadfaelbrew,ebouaziz/linuxbrew,ebouaziz/linuxbrew,SuperNEMO-DBD/cadfaelbrew,bukzor/linuxbrew,Linuxbrew/linuxbrew,Linuxbrew/linuxbrew,reelsense/linuxbrew,drbenmorgan/linuxbrew,saketkc/linuxbrew,reelsense/linuxbrew,Angeldude/linuxbrew,bukzor/linuxbrew,sjackman/linuxbrew,Linuxbrew/linuxbrew,drbenmorgan/linuxbrew,ebouaziz/linuxbrew,Angeldude/linuxbrew,drbenmorgan/linuxbrew,sjackman/linuxbrew,bukzor/linuxbrew,SuperNEMO-DBD/cadfaelbrew,sjackman/linuxbrew,drbenmorgan/linuxbrew,gnubila-france/linuxbrew,Homebrew/linuxbrew,DoomHammer/linuxbrew,Angeldude/linuxbrew,Angeldude/linuxbrew,Homebrew/linuxbrew,gnubila-france/linuxbrew,reelsense/linuxbrew,DoomHammer/linuxbrew,saketkc/linuxbrew,gnubila-france/linuxbrew,Homebrew/linuxbrew,DoomHammer/linuxbrew,sjackman/linuxbrew,SuperNEMO-DBD/cadfaelbrew,gnubila-france/linuxbrew,saketkc/linuxbrew