[Runner] Remove completely ${sysroot}/include from headers search paths for clang

Doesn't seem to be useful (it's empty for all platforms as far as I could see)
and it's in the default search path anyway:

```console
sandbox:${WORKSPACE} # /opt/x86_64-linux-musl/bin/clang -target ${target} --sysroot=/opt/${target}/${target}/sys-root -v -E -x c - < /dev/null
clang version 18.1.7 (/home/tim/.cache/BinaryBuilder/downloads/clones/llvm-project.git-1df819a03ecf6890e3787b27bfd4f160aeeeeacd50a98d003be8b0893f11a9be 768118d1ad38bf13c545828f67bd6b474d61fc55)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/x86_64-linux-musl/bin
 (in-process)
 "/opt/x86_64-linux-musl/bin/clang-18" -cc1 -triple aarch64-unknown-linux-gnu -E -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name - -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu generic -target-feature +v8a -target-feature +fp-armv8 -target-feature +neon -target-abi aapcs -debugger-tuning=gdb -fdebug-compilation-dir=/workspace -v -fcoverage-compilation-dir=/workspace -resource-dir /opt/x86_64-linux-musl/lib/clang/18 -isysroot /opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root -internal-isystem /opt/x86_64-linux-musl/lib/clang/18/include -internal-isystem /opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root/usr/local/include -internal-externc-isystem /opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root/include -internal-externc-isystem /opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root/usr/include -source-date-epoch 0 -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcolor-diagnostics -target-feature +outline-atomics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o - -x c -
clang -cc1 version 18.1.7 based upon LLVM 18.1.7 default target x86_64-alpine-linux-musl
ignoring nonexistent directory "/opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root/usr/local/include"
ignoring nonexistent directory "/opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root/include"
 /opt/x86_64-linux-musl/lib/clang/18/include
 /opt/aarch64-linux-gnu/aarch64-linux-gnu/sys-root/usr/include
End of search list.
```

Author: giordano

src/Runner.jl

@@ -476,10 +476,6 @@ function generate_compiler_wrappers!(platform::AbstractPlatform; bin_path::Abstr
                     "-isystem /opt/$(aatriplet(p))/$(aatriplet(p))/include",
                 ])
             end
-            # Extra stuff
-            append!(flags, [
-                # "-isystem /opt/$(aatriplet(p))/$(aatriplet(p))/sys-root/include", # <-- this directory doesn't exist out-of-the box (unless manually created to put libc++ in its subdirs, but this would remain without header files anyway), commenting out for the time being
-            ])
         end
 
         if Sys.iswindows(p) && nbits(p) == 32