Revert "x86: enable FORTIFY_SOURCE"

This reverts commit 93ab3b9e55f73526419de7fe1c6ce5e398da4387.
Revert "Export TARGET_GCC_VERSION as an env variable."

This reverts commit dee81638dc2a17383da95229fe211054f05ad032.
Revert "[ARM] Extend the usage of TARGET_GCC_VERSION for gdb and arm-eabi-*."

This reverts commit 84b5cbfa325bf57a90a962b1386f3f8215eaa4ad.
Revert "Add TARGET_GCC_VERSION"

This reverts commit 83bd4b7d48896486f28e0e687b2e4d99da02d749.