[Driver] Link Flang runtime on Solaris (llvm#65644)

I noticed that `flang-new` cannot link Fortran executables on Solaris since the runtime libs are missing.

This patch fixes this, following `Gnu.cpp`. The `linker-flags.f90` testcase is augmented to test for this,
renaming the `GNU` label to `UNIX` so it can be reused.  Also use the current form `--target=` in the tests
and join the `-l` lines in the test for readibility.

Tested on `amd64-pc-solaris2.11`, `sparcv9-sun-solaris2.11`, and
`x86_64-pc-linux-gnu`.

clang/lib/Driver/ToolChains/Solaris.cpp

@@ -222,6 +222,14 @@ void solaris::Linker::ConstructJob(Compilation &C, const JobAction &JA,
         getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
       CmdArgs.push_back("-lm");
     }
+    // Additional linker set-up and flags for Fortran. This is required in order
+    // to generate executables. As Fortran runtime depends on the C runtime,
+    // these dependencies need to be listed before the C runtime below.
+    if (D.IsFlangMode()) {
+      addFortranRuntimeLibraryPath(getToolChain(), Args, CmdArgs);
+      addFortranRuntimeLibs(getToolChain(), CmdArgs);
+      CmdArgs.push_back("-lm");
+    }
     if (Args.hasArg(options::OPT_fstack_protector) ||
         Args.hasArg(options::OPT_fstack_protector_strong) ||
         Args.hasArg(options::OPT_fstack_protector_all)) {

flang/test/Driver/linker-flags.f90

@@ -2,15 +2,16 @@
 ! invocation. These libraries are added on top of other standard runtime
 ! libraries that the Clang driver will include.
 
-! RUN: %flang -### -target ppc64le-linux-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,GNU
-! RUN: %flang -### -target aarch64-apple-darwin %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,DARWIN
-! RUN: %flang -### -target x86_64-windows-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,MINGW
+! RUN: %flang -### --target=ppc64le-linux-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,UNIX
+! RUN: %flang -### --target=aarch64-apple-darwin %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,DARWIN
+! RUN: %flang -### --target=sparc-sun-solaris2.11 %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,UNIX
+! RUN: %flang -### --target=x86_64-windows-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,MINGW
 
 ! NOTE: Clang's driver library, clangDriver, usually adds 'libcmt' and
 !       'oldnames' on Windows, but they are not needed when compiling
 !       Fortran code and they might bring in additional dependencies.
 !       Make sure they're not added.
-! RUN: %flang -### -target aarch64-windows-msvc -fuse-ld= %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,MSVC --implicit-check-not libcmt --implicit-check-not oldnames
+! RUN: %flang -### --target=aarch64-windows-msvc -fuse-ld= %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,MSVC --implicit-check-not libcmt --implicit-check-not oldnames
 
 ! Compiler invocation to generate the object file
 ! CHECK-LABEL: {{.*}} "-emit-obj"
@@ -21,12 +22,9 @@
 !       run on any other platform, such as Windows that use a .exe
 !       suffix. Clang's driver will try to resolve the path to the ld
 !       executable and may find the GNU linker from MinGW or Cygwin.
-! GNU-LABEL:  "{{.*}}ld{{(\.exe)?}}"
-! GNU-SAME: "[[object_file]]"
-! GNU-SAME: -lFortran_main
-! GNU-SAME: -lFortranRuntime
-! GNU-SAME: -lFortranDecimal
-! GNU-SAME: -lm
+! UNIX-LABEL:  "{{.*}}ld{{(\.exe)?}}"
+! UNIX-SAME: "[[object_file]]"
+! UNIX-SAME: "-lFortran_main" "-lFortranRuntime" "-lFortranDecimal" "-lm"
 
 ! DARWIN-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! DARWIN-SAME: "[[object_file]]"