meson: Remove _FORTIFY_SOURCE

Distributions want to override _FORTIFY_SOURCE, and various libc
implementations support different versions of it. This is causing us
some headaches, and supporting major platforms unfortunately need to
take priority.

Remove _FORTIFY_SOURCE and instead try to set -fhardened, which we can
easily detect, and enable a few extra errors for good measure.

Reference: mesonbuild/meson#13024
Reference: ossf/wg-best-practices-os-developers#659

Author: kennylevinsen

meson.build

@@ -51,7 +51,13 @@ add_project_arguments(cc.get_supported_arguments(
 		'-Wmissing-prototypes',
 		'-Wno-unknown-warning-option',
 		'-Wno-unused-command-line-argument',
+		'-Werror=strict-aliasing',
+		'-Werror=lto-type-mismatch',
+		'-Werror=odr',
 		'-Wvla',
+		# GCC warns if hardened is used without optimization
+		'-Wno-hardened',
+		'-fhardened',
 	]),
 	language: 'c',
 )
@@ -63,10 +69,6 @@ add_project_arguments(cc.get_supported_link_arguments(
 	language: 'c',
 )
 
-if ['debugoptimized', 'release', 'minsize'].contains(get_option('buildtype'))
-	add_project_arguments('-D_FORTIFY_SOURCE=2', language: 'c')
-endif
-
 if get_option('buildtype').startswith('debug')
 	add_project_arguments('-DDEBUG', language : 'c')
 endif