Support extra compiler flags during building (#39191)

Many Linux distributions like to use an extra set of compiler flags (via
`CFLAGS`, `CXXFLAGS` and `LDFLAGS`) to produce builds that are hardened
against vulnerabilities and exploits. The flags sometimes also enable
extra warnings to inform packagers about potential memory issues.

This pach adds support for that to dotnet/runtime.

The obvious method to make this work is to just export the `CFLAGS`,
`CXXFLAGS`, and `LDFLAGS` directly. This, however, enables those flags
during configure-time (aka `cmake` without `--build` too). That means
several cmake configure tests get executed with unexpected compiler
flags. These configure tests can then report incorrect results.

For example, https://bugzilla.redhat.com/show_bug.cgi?id=1712158
demonstrates an issue where the check for `strerror_r` in the runtime
comes to the wrong conclusion because `-Wall` is enabled and a variable
is unused.

A slightly longer fix is to support another set of environment
variables, and use them to set `CFLAGS`, `CXXFLAGS`, `LDFLAGS`, but only
for the invocation of `cmake --build`/`make`.

See #35727 for the complete details.

Fixes #35727

1 files changed, 3 insertions, 0 deletions

diff --git a/eng/build.sh b/eng/build.sh
index da8e3770f59..afa16a69447 100755
--- a/eng/build.sh
+++ b/eng/build.sh
@@ -97,6 +97,9 @@ usage()
   echo "* Build CoreCLR for Linux x64 on Debug configuration using GCC 8.4."
   echo "./build.sh clr -gcc8.4"
   echo ""
+  echo "* Build CoreCLR for Linux x64 using extra compiler flags (-fstack-clash-protection)."
+  echo "EXTRA_CFLAGS=-fstack-clash-protection EXTRA_CXXFLAGS=-fstack-clash-protection ./build.sh clr"
+  echo ""
   echo "* Cross-compile CoreCLR runtime for Linux ARM64 on Release configuration."
   echo "./build.sh clr.runtime -arch arm64 -c release -cross"
   echo ""