libsingular_julia: more platforms and make build deps explicit

The build dependencies on GMP_jll and MPFR_jll were only implicit so far,
but we need to make them explicit and with version constraints to avoid
issues on macOS (when this JLL is built against a too-new version of either
of these libraries, it becomes unloadable in older Julia versions)

L/libsingular_julia/build_tarballs.jl

@@ -8,6 +8,8 @@ const version = v"0.2.0"
 
 # Collection of sources required to build libsingular-julia
 const sources = [
+#    GitSource("https://github.com/oscar-system/libsingular-julia",
+#              "d88ee35e8a1cb10be271d1482ee7c8e3f108e2e4"),
     ArchiveSource("https://github.com/oscar-system/libsingular-julia/archive/v$(version).tar.gz",
                   "ee4e5ef96caf9d18553600d87f922e5d40cb1c7d30a1697c92b23b493498db1a"),
 ]
@@ -34,16 +36,9 @@ install_license $WORKSPACE/srcdir/libsingular-j*/LICENSE.md
 
 # These are the platforms we will build for by default, unless further
 # platforms are passed in on the command line
-const platforms = expand_cxxstring_abis([
-    Linux(:x86_64; libc=:glibc, compiler_abi=CompilerABI(cxxstring_abi=:cxx11)),
-    MacOS(:x86_64; compiler_abi=CompilerABI(cxxstring_abi=:cxx11)),
-    #Linux(:i686, libc=:glibc; compiler_abi=CompilerABI(cxxstring_abi=:cxx11)), # Wrapper code is buggy
-    #FreeBSD(:x86_64, compiler_abi=CompilerABI(cxxstring_abi=:cxx11)),
-])
-
-#platforms = supported_platforms()
-#platforms = filter!(!Sys.iswindows, platforms)
-#platforms = expand_cxxstring_abis(platforms)
+platforms = supported_platforms()
+platforms = filter!(!Sys.iswindows, platforms)
+platforms = expand_cxxstring_abis(platforms)
 
 # The products that we will ensure are always built
 const products = [
@@ -53,9 +48,11 @@ const products = [
 # Dependencies that must be installed before this package can be built
 const dependencies = [
     Dependency("CompilerSupportLibraries_jll"),
-    BuildDependency(PackageSpec(name="Julia_jll", version="v1.4.1")),
+    BuildDependency(PackageSpec(name="Julia_jll", version=v"1.4.1")),
     Dependency("libcxxwrap_julia_jll"),
     Dependency("Singular_jll"),
+    BuildDependency(PackageSpec(name="GMP_jll", version=v"6.1.2")),
+    BuildDependency(PackageSpec(name="MPFR_jll", version=v"4.0.2")),
 ]
 
 # Build the tarballs, and possibly a `build.jl` as well.