Define dirent d_type for Solaris based OS

[am11]

1. On Solaris-like operating systems such as SmartOS, struct dirent does not contain a member called d_type. Although we have a comment about it:

   runtime/src/installer/corehost/cli/hostmisc/pal.unix.cpp

   Line 837 in 5eda36e

   // Handle symlinks and file systems that do not support d_type

   but that itself is in a switch block over d_type. This delta defines d_type's DT_UNKNOWN and friends for Solaris.

2. _X is defined in one of the system header, so undef it before #define:

   /usr/include/iso/ctype_iso.h:60:0: note: this is the location of the previous definition
   #define _X 0x00000080 /* heXadecimal digit */
   

3. GCC build of installer was broken even on Linux, due to missing dl link in test project. Align it with what we are already using in src projects:

   runtime/src/installer/corehost/cli/common.cmake

   Line 44 in 5eda36e

   target_link_libraries (${DOTNET_PROJECT_NAME}"dl")

Contributes to #4173.

[am11]

With these changes:

src/installer/corehost/build.sh -apphostver "5.0.0-dev" -hostver "5.0.0-dev" \
-fxrver "5.0.0-dev" -policyver "5.0.0-dev" -commithash $(git rev-parse HEAD) -gcc

succeeds on SmartOS amd64. There is another layer of shared configuration for SunOS, which is based on top of #34211, I will create a separate PR once these are merged.

cc @jkotas

[am11]

Libraries tests failures are related to #28553.

[am11]

Resolved merge conflict and updated title to reflect what PR is doing now.

[lpereira]

LGTM with a suggestion

[am11]

@jkotas, seems like two CI legs are green on AzDo but GitHub hasn't sync in past two days:

• Build Windows_NT x64 debug Mono_Libraries: https://dev.azure.com/dnceng/public/_build/results?buildId=586901&view=logs&j=b3f28f68-bdae-5f1a-fb91-7b966fa6da48
• Mono Product Build Linux arm64 debug: https://dev.azure.com/dnceng/public/_build/results?buildId=586899&view=logs&j=d87e6e36-3792-5ccc-52f1-17008cc0feaf

System.Net.Security.Tests.ClientAsyncAuthenticateTest.ClientAsyncAuthenticate_ServerNoEncryption_NoConnect failure from Libraries Test Run release coreclr Windows_NT x86 Release leg seems unrelated, as PR does not touch Libraries (even :/eng/native/configurecompiler.cmake is not used by libraries - yet). However, there was no issue reported for it previously so I have filed #34545.