Make pointer-to-int-cast warnings non-fatal

Latest gcc on Debian unstable i386 starts to fail with

> tests/test-umockdev-vala.vala:714:19: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>     xfer[0].tx_buf = (uint64) tx_buf;

It's right -- this *is* an evil and wrong cast, but unfortunately Linux
defines the struct precisely as that -- `u64`, on all platforms. As we
can't selectively `#pragma` these away, disable the fatal warning
globally.

meson.build

@@ -41,6 +41,8 @@ add_project_arguments(
   cc.get_supported_arguments(
     # Vala doesn't have `const void*`, or a way to selectively #pragma these in the code
     '-Wno-error=discarded-qualifiers',
+    # spi_ioc_transfer.[rx]x_buf are pointers, but declared u64 everywhere; Vala can't selectively #pragma these
+    '-Wno-error=pointer-to-int-cast',
     # mostly const dropping and dropped "volatile" in fully autogenerated code;
     # upstream Vala does not support fixing this warning
     '-Wno-error=incompatible-pointer-types',

tests/test-umockdev-vala.vala

@@ -710,6 +710,7 @@ t_spidev_ioctl ()
   tx_buf[1] = 0xff;
 
   Posix.memset (xfer, 0, sizeof (Ioctl.spi_ioc_transfer) * 2);
+  /* these casts are evil, bad, and wrong -- but that's how Linux defines them, even 32 bit platforms have u64 */
   xfer[0].tx_buf = (uint64) tx_buf;
   xfer[0].len = 2;
   xfer[1].rx_buf = (uint64) rx_buf;