Unset _FORTIFY_SOURCE before setting it to fix error about redefinition

[sburton84]

When building for the x86_64-fortanix-unknown-sgx target in release mode I receive the following errors:

  <command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
  <built-in>: note: this is the location of the previous definition
  <command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
  <built-in>: note: this is the location of the previous definition
  cc1: all warnings being treated as errors

I think these would only be warnings but MBEDTLS_FATAL_WARNINGS defaults to ON which makes them into errors.

This patch fixes this by explicitly unsetting _FORTIFY_SOURCE before setting it to a new value.

[jethrogb]

Thanks for the PR!

I think we used to have -U but removed that for some reason, so I'm not immediately inclined to land this as is. Which C compiler are you using?

[sburton84]

Which C compiler are you using?

Currently using this version of GCC: gcc (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0

[jethrogb]

I think we used to have -U but removed that for some reason, so I'm not immediately inclined to land this as is.

Actually I misremembered. We do both in the build script for mbedtls, but not mbedtls-sys.

[sburton84]

The CI build failures seem to be due to an unrelated issue (rust-lang/rust#82730 I think)

[jethrogb]

bors try

[bors]

try

Build succeeded:

• continuous-integration/travis-ci/push

[jethrogb]

bors r+

[bors]

Build succeeded:

• continuous-integration/travis-ci/push