Improve the (cross-)build experience especially with LLVM (#353)

* Suppress clang warnings caused by boost headers

* Make binutils selectable via environment variables

Some build environments specify what tools to use via environment variables.

e.g. NM could be 'x86_64-unknown-linux-gnu-nm' when cross-compiling

* Use llvm-nm friendly non-short format value

LLVM's nm implementaion (llvm-nm) wants the entire string to match.
It doesn't allow just 'p' it wants 'posix'.

- https://github.com/llvm/llvm-project/blob/llvmorg-21.1.3/llvm/tools/llvm-nm/llvm-nm.cpp#L2435-L2448

The nm implementations from GNU binutils and FreeBSD parse the format
argument value only by looking at the first character.
They are accept both 'p' and 'posix'.

- https://github.com/bminor/binutils-gdb/blob/binutils-2_45/binutils/nm.c#L410-L438
- https://github.com/freebsd/freebsd-src/blob/release/14.3.0/contrib/elftoolchain/nm/nm.c#L506-L529

cmake/build_wrapper.sh

@@ -5,6 +5,9 @@ cleanup () {
     rm -f ${SYMSFILE} ${KEEPSYMS}
 }
 
+NM="${NM:-nm}"
+OBJCOPY="${OBJCOPY:-objcopy}"
+
 PREFIX=$1
 KEEPSYMS_IN=$2
 shift 2
@@ -25,12 +28,12 @@ if [ `uname` = "FreeBSD" ]; then
 fi
 cp ${KEEPSYMS_IN} ${KEEPSYMS}
 # get all symbols from libc and turn them into patterns
-nm ${NM_FLAG} p -g -D ${LIBC_SO} | sed 's/\([^ @]*\).*/^\1$/' >> ${KEEPSYMS}
+${NM} ${NM_FLAG} posix -g -D ${LIBC_SO} | sed 's/\([^ @]*\).*/^\1$/' >> ${KEEPSYMS}
 # build the object
 "$@"
 # rename the symbols in the object
-nm ${NM_FLAG} p -g ${OUT} | cut -f1 -d' ' | grep -v -f ${KEEPSYMS} | sed -e "s/\(.*\)/\1\ ${PREFIX}_\1/" >> ${SYMSFILE}
+${NM} ${NM_FLAG} posix -g ${OUT} | cut -f1 -d' ' | grep -v -f ${KEEPSYMS} | sed -e "s/\(.*\)/\1\ ${PREFIX}_\1/" >> ${SYMSFILE}
 if test -s ${SYMSFILE}
 then
-    objcopy --redefine-syms=${SYMSFILE} ${OUT}
+    ${OBJCOPY} --redefine-syms=${SYMSFILE} ${OUT}
 fi

cmake/cflags-generic.cmake

@@ -36,11 +36,9 @@ if(NETBSD)
     set(EXTRA_CXX_FLAGS "${EXTRA_CXX_FLAGS} -DHAVE_BUILTIN_POPCOUNT")
 endif()
 
-if(MACOSX)
-    # Boost headers cause such complains on MacOS
+# Boost headers cause such complains on MacOS or when building with LLVM toolchains
 set(EXTRA_C_FLAGS "${EXTRA_C_FLAGS} -Wno-deprecated-declarations -Wno-unused-parameter")
 set(EXTRA_CXX_FLAGS "${EXTRA_CXX_FLAGS} -Wno-deprecated-declarations -Wno-unused-parameter")
-endif()
 
 # these end up in the config file
 CHECK_C_COMPILER_FLAG(-fvisibility=hidden HAS_C_HIDDEN)