support/testing/tests/fs/test_iso9660.py: use a more recent toolchain

The ISO9660 tests are currently using an old 2017 toolchain. Let's
switch to a modern toolchain, which is regularly updated. Also, we use
a toolchain based on glibc since grub2 doesn't build with recent
uClibc toolchains.

It will work around build issues with syslinux.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/10975828975
  https://gitlab.com/buildroot.org/buildroot/-/jobs/10975828871
  https://gitlab.com/buildroot.org/buildroot/-/jobs/10975828770

(Even though those should be fixed separately, as syslinux should
continue to build with old compilers not supporting std=gnu17)

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

support/testing/tests/fs/test_iso9660.py

@@ -4,16 +4,9 @@ import infra.basetest
 
 BASIC_CONFIG = \
     """
-    BR2_x86_pentium4=y
+    BR2_x86_core2=y
     BR2_TOOLCHAIN_EXTERNAL=y
-    BR2_TOOLCHAIN_EXTERNAL_CUSTOM=y
-    BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD=y
-    BR2_TOOLCHAIN_EXTERNAL_URL="http://autobuild.buildroot.org/toolchains/tarballs/br-i386-pentium4-full-2017.05-1078-g95b1dae.tar.bz2"
-    BR2_TOOLCHAIN_EXTERNAL_GCC_6=y
-    BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_2=y
-    BR2_TOOLCHAIN_EXTERNAL_LOCALE=y
-    # BR2_TOOLCHAIN_EXTERNAL_HAS_THREADS_DEBUG is not set
-    BR2_TOOLCHAIN_EXTERNAL_CXX=y
+    BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_CORE2_GLIBC_STABLE=y
     BR2_TARGET_GENERIC_GETTY_PORT="ttyS0"
     BR2_TARGET_GENERIC_GETTY_BAUDRATE_115200=y
     BR2_LINUX_KERNEL=y