`Q_snprintf` was not declared in this scope; did you mean `V_snprintf`?

[clubby789]

Description

When building TC2 as described in the README, I get a number of errors related to Q_snprintf not being declared.

Checklist

• [x] None of the open or closed issues document this problem.
• [x] This is a bug, not a new idea.
• [x] This is objectively a bug, and not something that people commonly disagree on.
• [x] This issue occurs on the latest Team Comtress release, or the master branch.
• [ ] This issue occurs on the latest vanilla TF2 update.
• [x] This bug is in the code of the game, not in the textures, sounds, or other resources.
• [ ] This issue is listed on the Source 1 official bugtracker.
• [ ] This issue occurs with DirectX level 100.
• [x] This issue occurs when using no custom content.
• [ ] This issue occurs when using start_tf2.bat (or start_server.bat) with no custom launch options.
• [ ] This issue occurs when using a listen server (using the map command ingame).
• [ ] This issue occurs when using a dedicated server.
• [x] This bug is in the internal procedures or tooling (e.g. the build process).

Reproduction

1. Clone the repo
2. Run ./build.sh

Setup Details

Client Settings

• Server or client: Client
• Operating system: Linux clubby789 5.16.14-1-MANJARO #1 SMP PREEMPT Fri Mar 11 14:12:18 UTC 2022 x86_64 GNU/Linux
• Team Comtress version: 006753a1a63263e3512bccf064b2ca944f34b5bc
• Custom content: No
• Launch options: N/A

[clubby789]

In file included from vpc.h:24,
                 from macros.cpp:7:
../../public/tier1/fmtstr.h: In member function ‘void CNumStr::SetInt8(int8)’:
../../public/tier1/fmtstr.h:326:57: error: ‘Q_snprintf’ was not declared in this scope; did you mean ‘V_snprintf’?
  326 |         inline void SetInt8( int8 n8 )                  { Q_snprintf( m_szBuf, sizeof(m_szBuf), "%d", (int32)n8 ); }
      |                                                         ^~~~~~~~~~
      |                                                         V_snprintf
../../public/tier1/fmtstr.h: In member function ‘void CNumStr::SetUint8(uint8)’:
../../public/tier1/fmtstr.h:327:58: error: ‘Q_snprintf’ was not declared in this scope; did you mean ‘V_snprintf’?
  327 |         inline void SetUint8( uint8 un8 )               { Q_snprintf( m_szBuf, sizeof(m_szBuf), "%d", (int32)un8 ); }
      |                                                          ^~~~~~~~~~
      |                                                          V_snprintf
../../public/tier1/fmtstr.h: In member function ‘void CNumStr::SetInt16(int16)’:
../../public/tier1/fmtstr.h:328:58: error: ‘Q_snprintf’ was not declared in this scope; did you mean ‘V_snprintf’?
  328 |         inline void SetInt16( int16 n16 )               { Q_snprintf( m_szBuf, sizeof(m_szBuf), "%d", (int32)n16 ); }
      |                                                          ^~~~~~~~~~
      |                                                          V_snprintf

This continues for several hundred lines, all in fmtstr.h. The Q_.... macros are gated behind #if !defined( VSTDLIB_BACKWARD_COMPAT )