[icu] ICU port adds -lm in pkgconfig files for debug MSVC builds

[equeim]

Describe the bug
When ICU is built for Windows (MSVC) target with debug variant, its configure script adds -lm library to Libs.private property of pkgconfig files. As as I know, this library does not exist in MSVC toolchain. It is not used with dynamic linking, but static linking with pkgconfig results in linking error.

Environment

• OS: Windows
• Compiler: MSVC 19.29.30138

To Reproduce
Steps to reproduce the behavior:

1. ./vcpkg install icu:x64-windows-static pkgconf:x64-windows-static
2. Try to link to static ICU library by using pkgconfig
3. Try to build CMake project with following CMakeLists.txt: https://gist.github.com/equeim/851df8e69165e509d9a511d1071e5631,
   dummy main.cpp and following CMake configuration command:

cmake -S \path\to\source -B \path\to\build -GNinja -DCMAKE_TOOLCHAIN_FILE=\path\to\vcpkg\scripts\buildsystems\vcpkg.cmake -DVCPKG_TARGET_TRIPLET=x64-windows-static -DPKG_CONFIG_EXECUTABLE=\path\to\vcpkg\installed\x64-windows-static\tools\pkgconf\pkgconf.exe -DCMAKE_BUILD_TYPE=Debug

2. Observe linking error LINK : fatal error LNK1104: cannot open file 'm.lib'

Expected behavior
Statically linking ICU using pkgconfig should work.

Failure logs
build.log

Additional context
I believe that passing ac_cv_lib_m_floor=no to configure script in icu/portfile.cmake for MSVC toolchain fixes the issue but I don't know whether it is the correct solution.

[PhoebeHui]

@equeim, thanks for reporting this issue, I will take a look.

[equeim]

Here is log of passed test for libm in debug build:

configure:5384: checking for floor in -lm
configure:5409: cl.exe -o conftest.exe -nologo -W3 -utf-8 -MP -MTd -Z7 -Ob0 -Od -Xcompiler -RTC1 -W4 -W4 -DWIN32 -D_WINDOWS -D_DEBUG -LF:/projects/vcpkg/installed/x64-windows-static/debug/lib -LF:/projects/vcpkg/installed/x64-windows-static/debug/lib/manual-link conftest.c -lm  -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -lcomdlg32 -ladvapi32 >&5
conftest.c
F:\projects\vcpkg\buildtrees\icu\x64-windows-static-dbg\conftest.c(31) : warning C4702: unreachable code
LINK : conftest.exe not found or not built by the last incremental link; performing full link
cl : Command line warning D9035 : option 'o' has been deprecated and will be removed in a future release
cl : Command line warning D9025 : overriding '/W3' with '/W4'
cl : Command line warning D9002 : ignoring unknown option '-Xcompiler'
cl : Command line warning D9002 : ignoring unknown option '-LF:/projects/vcpkg/installed/x64-windows-static/debug/lib'
cl : Command line warning D9002 : ignoring unknown option '-LF:/projects/vcpkg/installed/x64-windows-static/debug/lib/manual-link'
cl : Command line warning D9002 : ignoring unknown option '-lm'
cl : Command line warning D9002 : ignoring unknown option '-lkernel32'
cl : Command line warning D9002 : ignoring unknown option '-luser32'
cl : Command line warning D9002 : ignoring unknown option '-lgdi32'
cl : Command line warning D9002 : ignoring unknown option '-lwinspool'
cl : Command line warning D9002 : ignoring unknown option '-lshell32'
cl : Command line warning D9002 : ignoring unknown option '-lole32'
cl : Command line warning D9002 : ignoring unknown option '-loleaut32'
cl : Command line warning D9002 : ignoring unknown option '-lcomdlg32'
cl : Command line warning D9002 : ignoring unknown option '-ladvapi32'
configure:5409: $? = 0
configure:5418: result: yes

And log of failed test for libm in release build:

configure:5384: checking for floor in -lm
configure:5409: cl.exe -o conftest.exe -nologo -W3 -utf-8 -MP -MT -O2 -Oi -Gy -Z7 -W4 -W4 -DWIN32 -D_WINDOWS -DNDEBUG -LF:/projects/vcpkg/installed/x64-windows-static/lib -LF:/projects/vcpkg/installed/x64-windows-static/lib/manual-link conftest.c -lm  -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -lcomdlg32 -ladvapi32 >&5
conftest.c
conftest.c(25): warning C4391: 'char floor()': incorrect return type for intrinsic function, expected 'double'
conftest.c(29): error C2168: 'floor': too few actual parameters for intrinsic function
cl : Command line warning D9035 : option 'o' has been deprecated and will be removed in a future release
cl : Command line warning D9025 : overriding '/W3' with '/W4'
cl : Command line warning D9002 : ignoring unknown option '-LF:/projects/vcpkg/installed/x64-windows-static/lib'
cl : Command line warning D9002 : ignoring unknown option '-LF:/projects/vcpkg/installed/x64-windows-static/lib/manual-link'
cl : Command line warning D9002 : ignoring unknown option '-lm'
cl : Command line warning D9002 : ignoring unknown option '-lkernel32'
cl : Command line warning D9002 : ignoring unknown option '-luser32'
cl : Command line warning D9002 : ignoring unknown option '-lgdi32'
cl : Command line warning D9002 : ignoring unknown option '-lwinspool'
cl : Command line warning D9002 : ignoring unknown option '-lshell32'
cl : Command line warning D9002 : ignoring unknown option '-lole32'
cl : Command line warning D9002 : ignoring unknown option '-loleaut32'
cl : Command line warning D9002 : ignoring unknown option '-lcomdlg32'
cl : Command line warning D9002 : ignoring unknown option '-ladvapi32'
configure:5409: $? = 2
configure: failed program was:
| /* confdefs.h */
| #define PACKAGE_NAME "ICU"
| #define PACKAGE_TARNAME "International Components for Unicode"
| #define PACKAGE_VERSION "69.1"
| #define PACKAGE_STRING "ICU 69.1"
| #define PACKAGE_BUGREPORT "http://icu-project.org/bugs"
| #define PACKAGE_URL "http://icu-project.org"
| #define STDC_HEADERS 1
| #define HAVE_SYS_TYPES_H 1
| #define HAVE_SYS_STAT_H 1
| #define HAVE_STDLIB_H 1
| #define HAVE_STRING_H 1
| #define HAVE_MEMORY_H 1
| #define HAVE_INTTYPES_H 1
| #define HAVE_STDINT_H 1
| #define SIZEOF_VOID_P 8
| /* end confdefs.h.  */
| 
| /* Override any GCC internal prototype to avoid an error.
|    Use char because int might match the return type of a GCC
|    builtin and then its argument prototype would still apply.  */
| #ifdef __cplusplus
| extern "C"
| #endif
| char floor ();
| int
| main ()
| {
| return floor ();
|   ;
|   return 0;
| }
configure:5418: result: no