meson: fix missing libm link on Fedora

[Copilot]

liblcms2_dep was declared without dependencies: deps, so m_dep (libm) and threads_dep were not propagated to consumers. Static library builds and certain linker configurations (e.g. --as-needed on Fedora) would fail to link executables because -lm never appeared in their link command.

Changes

• src/meson.build: add dependencies: deps to declare_dependency() so libm and pthreads are transitively carried to all consumers of liblcms2_dep

# before
liblcms2_dep = declare_dependency(
  link_with: liblcms2_lib,
  include_directories: [inc_dirs, include_directories('.')],
)

# after
liblcms2_dep = declare_dependency(
  link_with: liblcms2_lib,
  include_directories: [inc_dirs, include_directories('.')],
  dependencies: deps,
)