libc/CMakeLists.txt: `string sub-command REPLACE requires at least four arguments.`

[sylvestre]

Caused by this change: #125831

-- Targeting AArch64
CMake Error at /build/source/libc/CMakeLists.txt:54 (string):
  string sub-command REPLACE requires at least four arguments.

Full log:
https://llvm-jenkins.debian.net/job/llvm-toolchain-jammy-binaries/architecture=amd64,distribution=jammy,label=amd64/1939/console

[llvmbot]

@llvm/issue-subscribers-libc

Author: Sylvestre Ledru (sylvestre)

Caused by this change: https://github.com//issues/125831

-- Targeting AArch64
CMake Error at /build/source/libc/CMakeLists.txt:54 (string):
  string sub-command REPLACE requires at least four arguments.

if(LLVM_VERSION_MAJOR)
string(REPLACE "-" "" NS_LLVM_VERSION_SUFFIX ${LLVM_VERSION_SUFFIX})
set(default_namespace "_llvm_libc${LLVM_VERSION_MAJOR}${LLVM_VERSION_MINOR}${LLVM_VERSION_PATCH}_${NS_LLVM_VERSION_SUFFIX}")
endif()