Add compiler-generated global variable per source file [Issue #24]

[ningaraj44]

Description

This pull request addresses Issue #24 by adding a compiler-generated global variable for each source file compiled using LLVM.

A global variable of type const char* is created during the compilation of each source file.
The variable name is constructed by prefixing __cli_ to the source file name, where non-alphanumeric characters such as . and / are replaced with underscores.
This ensures uniqueness of the variable name across all translation units in a multi-file project.

These variables act as metadata anchors, preserving the origin filename through all stages of the build: IR generation, object file creation, and final linking.

---

Example:

If compiling test4.c, the following global will be emitted in the IR:

@__cli_test4_c = constant [8 x i8] c"test4.c\00"

If compiling test4.o, the following global will be emitted in the object file is :

0000000000000000 R __cli_test4_c

If compiling a.out, the following global will be emitted in the executable file is :

25: 0000000000000204     8 OBJECT  GLOBAL DEFAULT   16 __cli_test4_c

---

Commands to Reproduce the Global Variable Injection:

Generate LLVM IR from test4.c:

./build/bin/clang -emit-llvm -S test4.c -o test4.ll
cat test4.ll | grep __cli_

Output:

@__cli_test4_c = constant [8 x i8] c"test4.c\00"

Compile to object file and inspect symbol:

./build/bin/clang -c test4.c -o test4.o
nm test4.o | grep __cli_

Output:

0000000000000000 R __cli_test4_c

Link to executable and inspect symbol:

./build/bin/clang test4.o -o a.out
nm a.out | grep __cli_

Output:

0000000000000204 R __cli_test4_c

Inspect final binary with readelf:

readelf -s a.out | grep __cli_

Output:

25: 0000000000000204     8 OBJECT  GLOBAL DEFAULT   16 __cli_test4_c