Merge bitcoin/bitcoin#30744: doc: Fix typo in build-unix.md

e78551b doc: Fix typo in `build-unix.md` (Hennadii Stepanov)

Pull request description:

  Addresses bitcoin/bitcoin#30454 (comment).

ACKs for top commit:
  davidgumberg:
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  l0rinc:
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Tree-SHA512: a312a7718ac3fe4a9a204518f1306f4d4622b9c11e027f26960d15ac2e2380682604890a2ae4b874a28e0798f243f8226475cda3a8f468a1aa98df7ab26eea5f

Author: fanquake

doc/build-unix.md

@@ -34,7 +34,7 @@ For the default build type `RelWithDebInfo`, the default compile flags are
 
 Finally, clang (often less resource hungry) can be used instead of gcc, which is used by default:
 
-    cmake -B build -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_CC_COMPILER=clang
+    cmake -B build -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang
 
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