github actions: remove -D_FORTIFY_SOURCE declaration

Fix build. The error was:
<command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
<command-line>: note: this is the location of the previous definition

.github/workflows/build.yml

@@ -46,7 +46,7 @@ jobs:
         shell: bash
         run: |
           ./bootstrap
-          export CFLAGS="-Wall -Wextra -Wformat -Wformat-security -Wmissing-declarations -Wmissing-prototypes -Wold-style-definition -Wpointer-arith -Wredundant-decls -Wshadow -Wstrict-prototypes -Wswitch-enum -Wundef -Wuninitialized -Wunused -Wwrite-strings -Wmissing-noreturn -flto=auto -O2 -Wp,-D_FORTIFY_SOURCE=2"
+          export CFLAGS="-Wall -Wextra -Wformat -Wformat-security -Wmissing-declarations -Wmissing-prototypes -Wold-style-definition -Wpointer-arith -Wredundant-decls -Wshadow -Wstrict-prototypes -Wswitch-enum -Wundef -Wuninitialized -Wunused -Wwrite-strings -Wmissing-noreturn -flto=auto -O2"
           ./configure --disable-polkit ${{ matrix.configure_args }}
           make V=1
 

.github/workflows/build_meson.yml

@@ -37,7 +37,7 @@ jobs:
       - name: compile
         shell: bash
         run: |
-          export CFLAGS="-Wall -Wextra -Wformat -Wformat-security -Wmissing-declarations -Wmissing-prototypes -Wold-style-definition -Wpointer-arith -Wredundant-decls -Wshadow -Wstrict-prototypes -Wswitch-enum -Wundef -Wuninitialized -Wunused -Wwrite-strings -Wmissing-noreturn -flto=auto -O2 -Wp,-D_FORTIFY_SOURCE=2"
+          export CFLAGS="-Wall -Wextra -Wformat -Wformat-security -Wmissing-declarations -Wmissing-prototypes -Wold-style-definition -Wpointer-arith -Wredundant-decls -Wshadow -Wstrict-prototypes -Wswitch-enum -Wundef -Wuninitialized -Wunused -Wwrite-strings -Wmissing-noreturn -flto=auto -O2"
           meson setup builddir --werror
           cd builddir