[NFC][CFI] Remove unnecessary -rtlib=platform from tests (#136032)

Should allow to reland #135981

Author: vitalybuka

clang/test/Driver/sanitizer-ld.c

@@ -831,7 +831,7 @@
 
 // CFI requirements.
 // RUN: not %clang -fsanitize=cfi \
-// RUN:     --target=x86_64-unknown-linux -fuse-ld=ld -rtlib=platform \
+// RUN:     --target=x86_64-unknown-linux -fuse-ld=ld \
 // RUN:     -resource-dir=%S/Inputs/resource_dir \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:     -### %s 2>&1 \
@@ -841,7 +841,7 @@
 
 // CFI by itself does not link runtime libraries.
 // RUN: not %clang -fsanitize=cfi \
-// RUN:     --target=x86_64-unknown-linux -fuse-ld=ld -rtlib=platform \
+// RUN:     --target=x86_64-unknown-linux -fuse-ld=ld \
 // RUN:     -resource-dir=%S/Inputs/resource_dir \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:     -### %s 2>&1 \