[bolt] bolt_rt cmake configure fails when a custom sysroot is provided

[hiraditya]

Bolt's CMakeLists.txt doesn't take the C, CXX, ASM flags because of which compiler errors out during cmake configure.

error message:

InstalledDir: /usr/local/home/out/stage1-install/bin
 "/usr/local/home/out/stage1-install/bin/ld.lld" 
 --sysroot=/usr/local/home/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot 
 -pie --hash-style=gnu --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o cmTC_ec920 
 /usr/local/home/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot/usr/lib/Scrt1.o 
 /usr/local/home/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot/usr/lib/crti.o crtbeginS.o 
 -L/usr/local/home/out/stage1-install/bin/../lib/x86_64-unknown-linux-gnu 
 -L/usr/local/home/out/stage1-install/lib/clang/18/lib/x86_64-unknown-linux-gnu 
 -L/usr/local/home/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot/usr/lib 
 CMakeFiles/cmTC_ec920.dir/CMakeCCompilerABI.c.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed crtendS.o 
 /usr/local/home/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot/usr/lib/crtn.o
ld.lld: error: cannot open crtbeginS.o: No such file or directory
ld.lld: error: unable to find library -lgcc
ld.lld: error: unable to find library -lgcc_s
ld.lld: error: unable to find library -lgcc
ld.lld: error: unable to find library -lgcc_s
ld.lld: error: cannot open crtendS.o: No such file or directory
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.