[tests] add test for #pragma pack with gcc

tests/misc/dune

@@ -2,3 +2,9 @@
   (applies_to user_directories.unix.t)
   (enabled_if (and (= %{os_type} unix) (<> %{system} macos)))
 )
+
+(cram
+  (applies_to pragma-pack-gcc)
+  (enabled_if %{bin-available:gcc})
+  (deps pragma-pack.c pragma-pack-utils.h)
+)

tests/misc/pragma-pack-gcc.t

+Testing that the output produced by Eva and the execution of the binary
+compiled by GCC are identical, both on a 32-bit machdep and on a 64-bit one
+
+# Note: we cannot currently test this in Nix due to issues with multiStdenv
+#  $ frama-c pragma-pack.c -machdep gcc_x86_32 -eva -eva-msg-key=-summary | grep -A999 "eva:final-states" | grep -v "\[eva:final-states\]" | grep -v __retres > eva.res
+#  $ gcc -m32 pragma-pack.c -Wno-pragmas && ./a.out > gcc.res
+#  $ diff -B eva.res gcc.res # should be identical
+
+  $ frama-c pragma-pack.c -machdep gcc_x86_64 -eva -eva-msg-key=-summary | grep -A999 "eva:final-states" | grep -v "\[eva:final-states\]" | grep -v __retres > eva.res
+  $ gcc pragma-pack.c -Wno-pragmas && ./a.out > gcc.res
+  $ diff -B eva.res gcc.res # should be identical