Suppress -Wformat-truncation for older GCC

[am11]

Build was hitting an error since #92674:

$. docker run --rm -v$(pwd)/runtime:/runtime -e ROOTFS_DIR=/crossrootfs/x64 \
      mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-cross-illumos-20220531132048-f13d79e \
      /runtime/build.sh -c Release -os illumos -cross -gcc
...
   -- The C compiler identification is GNU 8.4.0
...
  [ 33%] Building C object System.Native/CMakeFiles/System.Native-Static.dir/pal_signal.c.o
  /runtime/src/native/libs/System.Globalization.Native/pal_icushim.c: In function 'OpenICULibraries.constprop':
/runtime/src/native/libs/System.Globalization.Native/pal_icushim.c(66,57): error G01DC61E5: 'snprintf' output may be truncated before the last format character [-Werror=format-truncation=] [/runtime/src/native/libs/build-native.proj]
           snprintf(symbolVersion, symbolVersionLen, "_%d%s", majorVer, suffix);
                                                           ^
  /runtime/src/native/libs/System.Globalization.Native/pal_icushim.c:66:9: note: 'snprintf' output between 3 and 49 bytes into a destination of size 38
           snprintf(symbolVersion, symbolVersionLen, "_%d%s", majorVer, suffix);
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This warning was introduced in gcc v7 and had bugs until v9.

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[tarekgh]

@am11 could you please merge the latest changes from main into your PR? Thanks!

[am11]

@tarekgh, done. Branch is up-to-date (modulo the merges made to the main branch in past two hours 😄).