FindBLAS/LAPACK: Add libblastrampoline support

libblastrampoline is a BLAS/LAPACK demuxing layer to allow selecting a
BLAS/LAPACK library at runtime.

Fixes: #25913

Help/release/dev/FindBLAS-LAPACK-libblastrampoline.rst

@@ -0,0 +1,5 @@
+FindBLAS-LAPACK-libblastrampoline
+---------------------------------
+
+* The :module:`FindBLAS` and :module:`FindLAPACK` modules gained
+  support for ``libblastrampoline``.

Modules/FindBLAS.cmake

@@ -164,6 +164,11 @@ BLAS/LAPACK Vendors
 
   Intel MKL v10+ 64 bit, single dynamic library
 
+``libblastrampoline``
+  .. versionadded:: 3.30
+
+  A BLAS/LAPACK demuxing library using PLT trampolines
+
 ``NVHPC``
   .. versionadded:: 3.21
 
@@ -1352,6 +1357,31 @@ if(BLA_VENDOR STREQUAL "NVHPC" OR BLA_VENDOR STREQUAL "All")
   unset(_blas_nvhpc_lib)
 endif()
 
+# libblastrampoline? (https://github.com/JuliaLinearAlgebra/libblastrampoline/tree/main)
+if(BLA_VENDOR STREQUAL "libblastrampoline" OR BLA_VENDOR STREQUAL "All")
+  set(_blas_libblastrampoline_lib "blastrampoline")
+
+  if(WIN32)
+    # Windows appends the version number to the library
+    string(APPEND _blas_libblastrampoline_lib "-5")
+  endif()
+
+  if(NOT BLAS_LIBRARIES)
+    check_blas_libraries(
+      BLAS_LIBRARIES
+      BLAS
+      sgemm
+      ""
+      "${_blas_libblastrampoline_lib}"
+      ""
+      ""
+      ""
+      )
+  endif()
+
+  unset(_blas_libblastrampoline_lib)
+endif()
+
 # Generic BLAS library?
 if(BLA_VENDOR STREQUAL "Generic" OR
    BLA_VENDOR STREQUAL "All")

Modules/FindLAPACK.cmake

@@ -742,6 +742,14 @@ if(NOT LAPACK_NOT_FOUND_MESSAGE)
     unset(_lapack_nvhpc_flags)
   endif()
 
+  # libblastrampoline? (https://github.com/JuliaLinearAlgebra/libblastrampoline/tree/main)
+  if(NOT LAPACK_LIBRARIES
+      AND (BLA_VENDOR STREQUAL "libblastrampoline" OR BLA_VENDOR STREQUAL "All"))
+    if(BLAS_LIBRARIES MATCHES "blastrampoline.+")
+      set(LAPACK_LIBRARIES ${BLAS_LIBRARIES})
+    endif()
+  endif()
+
   # Generic LAPACK library?
   if(NOT LAPACK_LIBRARIES
       AND (BLA_VENDOR STREQUAL "Generic"