Makefile: drop -pedantic from CFLAGS

Makefile: drop -pedantic from CFLAGS

With -pedantic enabled, -Werror causes build failures when we try to
call lwc_string_ref(). For example,

  src/svgtiny_css.c:120:9: error: use of GNU statement expression
  extension from macro expansion [-Werror,
  -Wgnu-statement-expression-from-macro-expansion]
  120 |         *abs = lwc_string_ref(rel);

will happen in the very next commit.