docs: Move -Cllvm-args forwarding explanation to tips.md

Author: harin-ramesh

Readme.md

@@ -159,7 +159,7 @@ $ LIBRARY_PATH="[gcc-path value]" LD_LIBRARY_PATH="[gcc-path value]" rustc +$(ca
 
  * _**CG_GCCJIT_DUMP_ALL_MODULES**_: Enables dumping of all compilation modules. When set to "1", a dump is created for each module during compilation and stored in `/tmp/reproducers/`.
  * _**CG_GCCJIT_DUMP_MODULE**_: Enables dumping of a specific module. When set with the module name, e.g., `CG_GCCJIT_DUMP_MODULE=module_name`, a dump of that specific module is created in `/tmp/reproducers/`.
- * _**CG_RUSTFLAGS**_: Send additional flags to rustc. Can be used to build the sysroot without unwinding by setting `CG_RUSTFLAGS=-Cpanic=abort`. Note that `-Cllvm-args` flags are forwarded to GCC.
+ * _**CG_RUSTFLAGS**_: Send additional flags to rustc. Can be used to build the sysroot without unwinding by setting `CG_RUSTFLAGS=-Cpanic=abort`.
  * _**CG_GCCJIT_DUMP_TO_FILE**_: Dump a C-like representation to /tmp/gccjit_dumps and enable debug info in order to debug this C-like representation.
  * _**CG_GCCJIT_DUMP_RTL**_: Dumps RTL (Register Transfer Language) for virtual registers.
  * _**CG_GCCJIT_DUMP_RTL_ALL**_: Dumps all RTL passes.

doc/tips.md

@@ -9,6 +9,14 @@ be useful.
 CG_RUSTFLAGS="-Clink-args=-save-temps -v" ../y.sh cargo build
 ```
 
+### How to send arguments to GCC
+
+The `-Cllvm-args` `rustc` flag is repurposed by `rustc_codegen_gcc` to pass arguments directly to the GCC backend. You can use it via the `CG_RUSTFLAGS` environment variable. For example, to pass a `-f` flag to GCC:
+
+```
+CG_RUSTFLAGS="-Cllvm-args=-fflag-name" ../y.sh cargo build
+```
+
 ### How to see the personality functions in the asm dump
 
 ```