build(meson): don't require python3 (#1267)

Thanks to abf3a67dd070e138c0f1a20b913abf003193cb79 the use of python3
isn't required anymore to configure the build, so I moved the
find_program('python3') inside the "if compile" block.

This makes it possible to configure cpp-httplib on systems where python
isn't available with tools like muon: https://sr.ht/~lattis/muon/

meson.build

@@ -19,7 +19,6 @@ project(
 # Check just in case downstream decides to edit the source
 # and add a project version
 version = meson.project_version()
-python3 = find_program('python3')
 if version == 'undefined'
   cxx = meson.get_compiler('cpp')
   version = cxx.get_define('CPPHTTPLIB_VERSION',
@@ -28,8 +27,6 @@ if version == 'undefined'
   assert(version != '', 'failed to get version from httplib.h')
 endif
 
-message('cpp-httplib version ' + version)
-
 deps = [dependency('threads')]
 args = []
 
@@ -64,6 +61,8 @@ endif
 cpp_httplib_dep = dependency('', required: false)
 
 if get_option('cpp-httplib_compile')
+  python3 = find_program('python3')
+
   httplib_ch = custom_target(
     'split',
     input: 'httplib.h',

meson_options.txt

@@ -5,5 +5,5 @@
 option('cpp-httplib_openssl', type: 'feature', value: 'auto', description: 'Enable OpenSSL support')
 option('cpp-httplib_zlib',    type: 'feature', value: 'auto', description: 'Enable zlib support')
 option('cpp-httplib_brotli',  type: 'feature', value: 'auto', description: 'Enable Brotli support')
-option('cpp-httplib_compile', type: 'boolean', value: false,  description: 'Split the header into a compilable header & source file')
+option('cpp-httplib_compile', type: 'boolean', value: false,  description: 'Split the header into a compilable header & source file (requires python3)')
 option('cpp-httplib_test',    type: 'boolean', value: false,  description: 'Build tests')