The official Audacity download has an exe built for XP (subsystem 5.01), but it uses wxWidgets DLLs built for Vista and later (subsystem 6.00). Presumably, the 2.1.2 wx DLLs were built with the default VS2013 C++ configuration, v120 whereas the Audacity was built with v120_xp. If so, then they were likely built with different SDKs. Mixing such things is not, to the best of my understanding, something supported by Microsoft.
One way to avoid this problem is to build wxWidgets with the v120_xp configuration. A diff against wxWidgets v3.1.0 can be found here: props.diff. The build system is different for earlier versions wxWidgets, so the change isn’t as localized, but the idea is the same: the "v120"s need to become "v120_xp"s.
Alternately, one could drop XP support.
Here’s truncated dumpbin output from some of the files in the 2.1.2 download (note the “subsystem version”):
audacity-win-2.1.2\Audacity>dumpbin /headers audacity.exe
Microsoft (R) COFF/PE Dumper Version 14.00.23918.0
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file audacity.exe
PE signature found
File Type: EXECUTABLE IMAGE
FILE HEADER VALUES
14C machine (x86)
5 number of sections
5691052F time date stamp Sat Jan 9 06:03:43 2016
0 file pointer to symbol table
0 number of symbols
E0 size of optional header
103 characteristics
Relocations stripped
Executable
32 bit word machine
OPTIONAL HEADER VALUES
10B magic # (PE32)
12.00 linker version
48D400 size of code
49B200 size of initialized data
0 size of uninitialized data
425600 entry point (00825600)
1000 base of code
48F000 base of data
400000 image base (00400000 to 00D2BFFF)
1000 section alignment
200 file alignment
5.01 operating system version
0.00 image version
5.01 subsystem version
audacity-win-2.1.2\Audacity>dumpbin /headers wxmsw30u_core_vc_custom.dll
Microsoft (R) COFF/PE Dumper Version 14.00.23918.0
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file wxmsw30u_core_vc_custom.dll
PE signature found
File Type: DLL
FILE HEADER VALUES
14C machine (x86)
5 number of sections
5679D100 time date stamp Tue Dec 22 15:38:56 2015
0 file pointer to symbol table
0 number of symbols
E0 size of optional header
2102 characteristics
Executable
32 bit word machine
DLL
OPTIONAL HEADER VALUES
10B magic # (PE32)
12.00 linker version
22EC00 size of code
223000 size of initialized data
0 size of uninitialized data
1FF64D entry point (101FF64D)
1000 base of code
230000 base of data
10000000 image base (10000000 to 10454FFF)
1000 section alignment
200 file alignment
6.00 operating system version
0.00 image version
6.00 subsystem version