Clang builds fail on Windows.

[dapperfu]

First attempt:

C:\Projects\openlibm>make USECLANG=1
clang   -fno-builtin -fno-strict-aliasing -O3 -fPIC -m64 -std=c99 -Wall -IC:/Projects/openlibm -IC:/Projects/openlibm/include -IC:/Projects/openlibm/amd64 -IC:/Projects/openlibm/src -DASSEMBLER -D__BSD_VISIBLE -Wno-implicit-function-declaration -IC:/Projects/openlibm/ld80 -c src/e_acos.c -o src/e_acos.c.o
clang.exe: error: unsupported option '-fPIC' for target 'x86_64-pc-windows-msvc'
make: *** [Make.inc:139: src/e_acos.c.o] Error 1

Then commenting out -fPIC:

C:\Projects\openlibm>make USECLANG=1
clang   -fno-builtin -fno-strict-aliasing -O3 -m64 -std=c99 -Wall -IC:/Projects/openlibm -IC:/Projects/openlibm/include -IC:/Projects/openlibm/amd64 -IC:/Projects/openlibm/src -DASSEMBLER -D__BSD_VISIBLE -Wno-implicit-function-declaration -IC:/Projects/openlibm/ld80 -c src/e_acos.c -o src/e_acos.c.o
src/e_acos.c:110:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
__weak_reference(acos, acosl);
^
src/e_acos.c:110:18: error: a parameter list without types is only allowed in a function definition
__weak_reference(acos, acosl);
                 ^
1 warning and 1 error generated.
make: *** [Make.inc:139: src/e_acos.c.o] Error 1

Toolchain:

• Windows 10 LTSB.
• LLVM from llvm.org: http:https://releases.llvm.org/download.html
• nuwin MinGW: https://nuwen.net/mingw.html

C:\Projects\openlibm>uname -a
MSYS_NT-10.0 DESKTOP-BS1LGM3 2.10.0(0.325/5/3) 2018-06-13 23:34 x86_64 Msys

[ViralBShah]

Enabled and tested in CI in #243 now.