Explicitly select linker for some mixed language libraries.

If no linker preference is set for a shared library, CMake is choosing
the executable that is used for linking based on the highest linker
preference value. If a library consists of C and Fortran sources, the
Fortran compiler frontend has the higher linker preference value and it
is chosen by default.

For the Intel oneAPI compiler with MSVC-like syntax `icx-cl` as
the C and C++ compiler and the Intel oneAPI Fortran compilers `ifort`
or `ifx`, this leads to the following situation in combination with
`WINDOWS_EXPORT_ALL_SYMBOLS`:
* The symbols that are to be exported from the library are collected from
the C objects and written to a `.def` file.
* Flags are generated that pass that `.def` file to the linker. However,
the syntax for these flags match the C compiler `icx-cl`.
* The Fortran compiler is used for linking (higher linker preference
value). But `.def` files need to be passed differently for `ifx` or
`ifort` than for `icx-cl`.
* That leads to the linked libraries being empty or only exporting the
Fortran symbols.

Explicitly specify to use the C compiler frontend as the linker for the
AMD and CHOLMOD libraries to work around that issue.

Fixes #799.

AMD/CMakeLists.txt

@@ -90,7 +90,8 @@ if ( BUILD_SHARED_LIBS )
         OUTPUT_NAME amd
         SOVERSION ${AMD_VERSION_MAJOR}
         PUBLIC_HEADER "Include/amd.h"
-        WINDOWS_EXPORT_ALL_SYMBOLS ON )
+        WINDOWS_EXPORT_ALL_SYMBOLS ON
+        LINKER_LANGUAGE C )
 
     if ( ${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.25" )
         set_target_properties ( AMD PROPERTIES EXPORT_NO_SYSTEM ON )
@@ -111,7 +112,8 @@ if ( BUILD_STATIC_LIBS )
         C_STANDARD 11
         C_STANDARD_REQUIRED ON
         OUTPUT_NAME amd
-        PUBLIC_HEADER "Include/amd.h" )
+        PUBLIC_HEADER "Include/amd.h"
+        LINKER_LANGUAGE C )
 
     if ( MSVC OR ("${CMAKE_C_SIMULATE_ID}" STREQUAL "MSVC") )
         set_target_properties ( AMD_static PROPERTIES

CHOLMOD/CMakeLists.txt

@@ -383,7 +383,8 @@ if ( BUILD_SHARED_LIBS )
         OUTPUT_NAME cholmod
         SOVERSION ${CHOLMOD_VERSION_MAJOR}
         PUBLIC_HEADER "Include/cholmod.h"
-        WINDOWS_EXPORT_ALL_SYMBOLS ON )
+        WINDOWS_EXPORT_ALL_SYMBOLS ON
+        LINKER_LANGUAGE C )
 
     if ( CHOLMOD_HAS_CUDA )
         set_target_properties ( CHOLMOD PROPERTIES CUDA_SEPARABLE_COMPILATION ON )
@@ -410,7 +411,8 @@ if ( BUILD_STATIC_LIBS )
         C_STANDARD 11
         C_STANDARD_REQUIRED ON
         OUTPUT_NAME cholmod
-        PUBLIC_HEADER "Include/cholmod.h" )
+        PUBLIC_HEADER "Include/cholmod.h"
+        LINKER_LANGUAGE C )
 
     if ( MSVC OR ("${CMAKE_C_SIMULATE_ID}" STREQUAL "MSVC") )
         set_target_properties ( CHOLMOD_static PROPERTIES