@cxx/ClassCns.cxx:execves Reuse Termux LD_PRELOAD

  as workaround (for termux-play-store/termux-issues#24
  termux/termux-app#2155
  termux/termux-app#4037 ).

Fixes
```
~/SubStack $ ./a.out
cxx/Macros.hxx: pass
execves(): pass
execvex(): pass
virusAnalysisTestsThrows(): pass
assistantCnsTestsThrows(): /data/data/com.termux/files/usr/bin/sh: 1: wget: Permission denied /data/data/com.termux/files/usr/bin
```
, (to
```
conversationCnsTestsThrows(): --2024-06-15 18:22:01--  https://stackoverflow.com/robots.txt
Resolving stackoverflow.com (stackoverflow.com)... 172.64.155.249, 104.18.32.7
Connecting to stackoverflow.com (stackoverflow.com)|172.64.155.249|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/plain]
Saving to: ‘robots.txt’

robots.txt                                   [ <=>                                                                              ]   1.99K  --.-KB/s    in 0.07s

2024-06-15 18:22:02 (27.4 KB/s) - ‘robots.txt’ saved [2036]

```
, as was)

cxx/ClassCns.cxx

@@ -5,6 +5,8 @@
 #include <vector> /* std::vector */
 #include <ctype.h> /* size_t */
 #ifdef _POSIX_VERSION
+#include <stdlib.h> /* getenv */
+#include <stdio.h> /* asprintf */
 #include <unistd.h> /* execve fork EXIT_FAILURE */
 #include <sys/wait.h> /* waitpid */
 #endif /* def _POSIX_VERSION */
@@ -31,6 +33,16 @@ const int execves(const std::vector<const std::string> &argvS, const std::vector
 	for(auto x = envpSmutable.begin(); envpSmutable.end() != x; ++x) {
 		envp.push_back(const_cast<char *>(x->c_str()));
 	}
+	if(envp.empty()) {
+		char* ld_preload = getenv("LD_PRELOAD");
+		if (ld_preload) {
+			// Keep LD_PRELOAD, necessary for now on the Google Play build of Termux.
+			char* ld_preload_env;
+			int allocated_bytes = asprintf(&ld_preload_env, "LD_PRELOAD=%s", ld_preload);
+			assert(allocated_bytes > 0);
+			envp.push_back(ld_preload_env);
+		}
+	}
 	envp.push_back(NULL);
 	execve(argv[0], &argv[0], &envp[0]); /* NORETURN */
 	exit(EXIT_FAILURE);