clang-8: error: unknown argument: '-flto-partition=none' when building lxml

When I build with clang/linux I'm now seeing the following error:

Building lxml version 4.1.1.
Building without Cython.
Using build configuration of libxslt 1.1.32
Building against libxml2/libxslt in the following directory: /usr/lib
...
clang -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -march=x86-64 -mtune=generic 
-O2 -pipe -fstack-protector-strong -fno-plt -flto -fuse-linker-plugin -ffat-lto-objects 
-flto-partition=none -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt 
-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt -fPIC 
-DCYTHON_CLINE_IN_TRACEBACK=1 -I/usr/include/libxml2 -Isrc -Isrc/lxml/includes 
-I/usr/include/python3.7m -c src/lxml/etree.c -o build/temp.linux-x86_64-3.7/src/lxml/etree.o -w
clang-8: error: unknown argument: '-flto-partition=none'
Compile failed: command 'clang' failed with exit status 1
creating tmp
cc -I/usr/include/libxml2 -I/usr/include/libxml2 -c /tmp/xmlXPathInit8q3851b_.c -o 
tmp/xmlXPathInit8q3851b_.o
/tmp/xmlXPathInit8q3851b_.c:2:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
 main (int argc, char **argv) {
 ^~~~
cc tmp/xmlXPathInit8q3851b_.o -L/usr/lib -lxml2 -o a.out
error: command 'clang' failed with exit status 1
make[1]: *** [/core/external/lxml/ExternalProject_lxml.mk:25: 
/core/workdir/ExternalProject/lxml/build] Error 1
make[1]: *** Waiting for unfinished jobs....
make: *** [Makefile:286: build] Error 2

I could be wrong, but I believe this error showed up when I updated my core OS. (Arch) I tried and 
older version of clang and an older version of the LibreOffice that used to compile and I'm now 
seeing this error there too.