For context, the issue that this PR fixes only happens when meson.get_cross_property() finds an existing value.

In all such cases, versions of Meson before 0.60.0 would print the following warning:

meson.build:338: WARNING: Trying to compare values of different types (list, bool) using ==.
The result of this is undefined and will become a hard error in a future Meson release.
Compiler for C supports arguments -fPIC: YES 
meson.build:352: WARNING: Trying to compare values of different types (list, bool) using ==.
The result of this is undefined and will become a hard error in a future Meson release.

Tested with the following cross file:

[binaries]
c = 'gcc'
cpp = 'g++'
pkgconfig = 'pkg-config'

[properties]
perl_ccopts = ['-D_REENTRANT', '-D_GNU_SOURCE', '-fwrapv', '-fno-strict-aliasing', '-pipe', '-fstack-protector-strong', '-I/usr/local/include', '-D_LARGEFILE_SOURCE', '-D_FILE_OFFSET_BITS=64', '-D_FORTIFY_SOURCE=2', '-I/usr/lib/perl5/5.34/core_perl/CORE']
perl_ldopts = ['-Wl,-E', '-Wl,-rpath,/usr/lib/perl5/5.34/core_perl/CORE', '-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now', '-fstack-protector-strong', '-L/usr/local/lib', '-L/usr/lib/perl5/5.34/core_perl/CORE', '-lperl', '-lpthread', '-ldl', '-lm', '-lcrypt', '-lutil', '-lc']

Note: the warning has been there since 0.44.0, and as I pointed out in IRC:

• the intended goal of this sentinel value was to check if a cross property is defined, but it was wrong if someone decided to define it in their cross file as perl_ccopts = false
• Meson 0.58 deprecates get_cross_property and replaces it with get_external_property... which comes with a has_external_property that does what you actually want.

Rather than bumping the minimum version of Meson to 0.58, it may be practical to wrap this in meson.version().version_compare() to use the new mechanism (the old mechanism can use whichever sentinel value it likes, since false will just be a Meson warning).

Also relevant :(
Perl/perl5#14030