build-llvm: Bump to llvmorg-13.0.0

In addition to the changes in 13.0.0 RC1 (listed in
9188cce), the following changes
relevant to llvm-mingw were made:

- Allow specifying language to llvm-rc with an 0x prefix
- Let the last specified option of -mconsole/-mwindows take effect
- Support both "--opt value" and "--opt=value" for more options in lld
- Add support for the --disable-dynamicbase option spelling in lld,
  in addition to the old existing --no-dynamicbase
- Fix linking with when enabling profiling

Author: mstorsjo

build-llvm.sh

@@ -16,7 +16,7 @@
 
 set -e
 
-: ${LLVM_VERSION:=llvmorg-13.0.0-rc1}
+: ${LLVM_VERSION:=llvmorg-13.0.0}
 ASSERTS=OFF
 unset HOST
 BUILDDIR="build"