lang/ruby26: fix build on powerpc

powerpc requires GCC after all to build this port:
building .ext/include/powerpc-freebsd13/rb_mjit_min_header-2.6.5.h
./miniruby -I./lib -I. -I.ext/common ./tool/transform_mjit_header.rb "cc " rb_mjit_header.h .ext/include/powerpc-freebsd13/rb_mjit_min_header-2.6.5.h

• Signal 6