Revert "[libc] build with -Werror (llvm#73966)"

This reverts commit 6066530.

Post submit buildbots are now red. We can use these explicit errors to better
clean up existing warnings, then reland this.

Link: llvm#73966

libc/cmake/modules/LLVMLibCObjectRules.cmake

@@ -43,10 +43,6 @@ function(_get_common_compile_options output_var flags)
     list(APPEND compile_options "-fno-rtti")
     list(APPEND compile_options "-Wall")
     list(APPEND compile_options "-Wextra")
-    # -DLIBC_WNO_ERROR=ON if you can't build cleanly with -Werror.
-    if(NOT LIBC_WNO_ERROR)
-      list(APPEND compile_options "-Werror")
-    endif()
     list(APPEND compile_options "-Wconversion")
     list(APPEND compile_options "-Wno-sign-conversion")
     list(APPEND compile_options "-Wimplicit-fallthrough")

libc/docs/dev/code_style.rst

@@ -178,11 +178,3 @@ these functions do not call the constructors and destructors of the
 allocated/deallocated objects. So, use these functions carefully and only
 when it is absolutely clear that constructor and destructor invocation is
 not required.
-
-Warnings in sources
-===================
-
-We expect contributions to be free of warnings from the `minimum supported
-compiler versions`__ (and newer).
-
-.. __: https://libc.llvm.org/compiler_support.html#minimum-supported-versions