Add support for unwinding the stack on 32-bit arm platforms (armv6, armv7) (#54)

This is a simple mod suggested by @weissi that now works thanks to
supporting DWARF v3 properly in #53. Tested with a Raspberry Pi 3B+
running Ubuntu 22.04 for armv7.

Author: jessezamora

Sources/CProfileRecorderSampler/fp_unwinder.c

@@ -76,6 +76,11 @@ int swipr_fp_unwinder_getcontext(struct swipr_fp_unwinder_context *context, ucon
     intptr_t reg_ip = uc->uc_mcontext.pc;
     intptr_t reg_fp = uc->uc_mcontext.regs[29];
     intptr_t reg_sp = uc->uc_mcontext.sp;
+#elif defined(__linux__) && defined(__arm__)
+    // ARM (32-bit) on Linux (e.g. ARMv6 and ARMv7)
+    intptr_t reg_ip = uc->uc_mcontext.arm_pc;
+    intptr_t reg_fp = uc->uc_mcontext.arm_fp;  // r11 is the frame pointer
+    intptr_t reg_sp = uc->uc_mcontext.arm_sp;  // r13 is the stack pointer
 #elif defined(__APPLE__) && defined(__x86_64__)
     intptr_t reg_ip = uc->uc_mcontext->__ss.__rip;
     intptr_t reg_fp = uc->uc_mcontext->__ss.__rbp;