meson: add explicit option for eclib support

Add an entry to meson.options (and tweak src/meson.build) so that
the user can explicitly state whether or not he would like eclib
support to be enabled, e.g.

  $ meson setup -Declib=disabled

The default of "auto" is backwards-compatible.

Author: orlitzky

meson.options

@@ -41,6 +41,13 @@ option(
   description: 'Coxeter 3.x interface to Coxeter groups'
 )
 
+option(
+  'eclib',
+  type: 'feature',
+  value: 'auto',
+  description: 'eclib interface to mwrank and elliptic curves over Q'
+)
+
 option(
   'mcqd',
   type: 'feature',

src/meson.build

@@ -157,7 +157,12 @@ mtx = cc.find_library(
 )
 png = dependency(['libpng', 'png', 'png16'], version: '>=1.2')
 zlib = dependency('zlib', version: '>=1.2.11')
-ec = dependency('eclib', version: '>=20250122', required: false, disabler: true)
+ec = dependency(
+  'eclib',
+  version: '>=20250122',
+  required: get_option('eclib'),
+  disabler: true
+)
 ecm = cc.find_library('ecm', required: not is_windows, disabler: true)
 gmpxx = dependency('gmpxx', required: not is_windows, disabler: true)
 fflas = dependency(