Fix rustc_codegen_gcc lto issue

Author: GuillaumeGomez

src/ci/docker/host-x86_64/x86_64-gnu-llvm-15/Dockerfile

@@ -37,6 +37,8 @@ RUN sh /scripts/sccache.sh
 
 # Make `libgccjit.so` accessible.
 RUN ln -s /usr/lib/gcc/x86_64-linux-gnu/12/libgccjit.so /usr/lib/x86_64-linux-gnu/libgccjit.so
+# Fix rustc_codegen_gcc lto issues.
+ENV GCC_EXEC_PREFIX="/usr/lib/gcc/"
 
 # We are disabling CI LLVM since this builder is intentionally using a host
 # LLVM, rather than the typical src/llvm-project LLVM.

src/ci/docker/host-x86_64/x86_64-gnu-tools/Dockerfile

@@ -64,6 +64,8 @@ RUN sh /scripts/sccache.sh
 
 # Make `libgccjit.so` accessible.
 RUN ln -s /usr/lib/gcc/x86_64-linux-gnu/12/libgccjit.so /usr/lib/x86_64-linux-gnu/libgccjit.so
+# Fix rustc_codegen_gcc lto issues.
+ENV GCC_EXEC_PREFIX="/usr/lib/gcc/"
 
 COPY host-x86_64/x86_64-gnu-tools/checktools.sh /tmp/