[Runner] Work around wrong path of compiler libraries for riscv64. Again (#407)

* [Runner] Work around wrong path of compiler libraries for riscv64. Again

* Add test of linking C++ library with gcc

* [Runner] Fix FreeBSD and add comment to explain why these flags are here

Author: giordano

src/Runner.jl

@@ -581,7 +581,13 @@ function generate_compiler_wrappers!(platform::AbstractPlatform; bin_path::Abstr
             # the wrappers before any additional arguments because we want this path to have
             # precedence over anything else.  In this way for example we avoid libraries
             # from `CompilerSupportLibraries_jll` in `${libdir}` are picked up by mistake.
-            dir = "/opt/$(aatriplet(p))/$(aatriplet(p))/lib" * (nbits(p) == 32 ? "" : "64")
+            # Note 2: Compiler libraries for riscv64 ended up in `lib/` for some reason, and
+            # are always in `lib/` for FreeBSD.
+            # Note 3: while these are technically link-only flags, link-only flags are
+            # written out in our wrappers as "post flags" after those passed on the command
+            # line, but we really need to have these flags before those to solve
+            # <https://github.com/JuliaPackaging/BinaryBuilderBase.jl/issues/163>.
+            dir = "/opt/$(aatriplet(p))/$(aatriplet(p))/lib" * (nbits(p) == 32 || arch(p) == "riscv64" || Sys.isfreebsd(p) ? "" : "64")
             append!(flags, ("-L$(dir)", "-Wl,-rpath-link,$(dir)"))
         end
         if lock_microarchitecture

test/runners.jl

@@ -220,11 +220,17 @@ end
                     std::complex<double> z3 = add(std::complex<double>(1.,2.),std::complex<double>(4.,2.));
                     return 0;
                 }
-            """
+                """
+            main_c = """
+                int main(void) {
+                    return 0;
+                }
+                """
             test_script = """
                 set -e
                 echo '$(test_cpp)' > test.cpp
                 echo '$(main_cpp)' > main.cpp
+                echo '$(main_c)' > main.c
                 # Make sure setting `CCACHE` doesn't affect the compiler wrappers.
                 export CCACHE=pwned
                 export USE_CCACHE=true
@@ -238,6 +244,10 @@ end
                 $(linker) -o main main.o test.o
                 # Link main program with shared library
                 $(linker) -o main main.o -L. -ltest
+
+                # Also make sure we can link to libtest (which may link to
+                # libstdc++) with gcc (as in the C compiler).
+                gcc -o main_c main.c -ltest -L.
                 """
             cmd = `/bin/bash -c "$(test_script)"`
             @test run(ur, cmd, iobuff; tee_stream=devnull)